Week 1: Basic Shortbread Tart Dough, Pâte Sablée

Pâte Sablée, or shortbread, is one of the classic french doughs. It can be used for tarts, cookies, and other dessert bases. The great thing about tarts is that once you have a shell, you can fill them with whatever you want: curds, custards, fruit, etc. Anything your heart desires!

A good Pâte Sablée should be slightly sweet and melt in your mouth. For tarts, it also has to be strong enough to survive being taken out of the tart pan, which poses an additional challenge. It typically contains butter, sugar, egg yolk, and flour, but other additions and variations are common. In my research, I have come across a lot of lore about tart dough, so I'm excited to see what actually holds up.

Research

To begin understanding a recipe, my first step is to see what recipes are already out there and use them as a starting point. I want to know what the commonalities and variations between these recipes are and what effects those have on the final product. What makes a tender tart shell tender? How do the ingredients affect the flavor and the structure? What is essential versus optional? How do the rules hold up to scientific rigor?

At first glance, recipes can look wildly different because they all make different amounts and use different units of measurement, but if you can normalize by a key ingredient, you can often start to find trends. The recipes I found for Pâte Sablée all had varying levels of egg, flour, and sugar, but the amount of butter was relatively constant across many recipes. I thus decided to normalize the recipes by the amount of butter in the recipe. Here are the results:

Table 1: Normalized Recipes [1, 2, 3, 4, 5, 6, 7]. You should use a scale to measure ingredients whenever possible to ensure consistency between bakes. Note 14 g is ~1 egg yolk.

Now we can see that the recipes generally fall into three categories: (1) high egg content, high sugar [4, 5], (2) moderate egg content, low sugar [1, 2, 3], and (3) low/no egg content, moderate sugar [6, 7]. It's really cool how close these recipes end up being, and it will be really interesting to look into the differences between these and unravel what is going on!

Generalized Technique

When testing, we only want to vary one variable at a time. There is a lot of variation in the salt and vanilla content in the recipes I found. In this recipe, these should mainly affect the overall flavor of the final product, so I'm just going to pick some middle of the road values for these and keep it uniform in all the tests: 1/4 tsp fine table salt and 1 tsp of vanilla.

Each recipe also has different mixing techniques, rolling techniques, baking temperatures, and baking times. For the first batch of tests, I'm going to use soft butter as in the traditional French method and mix the butter, salt, vanilla, and sugar together. Then I'll mix in the egg, followed by the flour. I'll mix in the flour until it is mostly incorporated then turn it out on the counter and Fraiser the dough to make sure the dough is uniform without overworking it. To fraiser dough, you smear a portion of the dough in one direction on your work surface with a dough scraper. Then you scrape up the dough that was smeared out and put it in a separate pile. You repeat this until all the dough has been fraisered. A few recipes call for whipping the butter. The main reason we'd want to whip butter is to make the final product lighter, so I will play around with this in future tests once I'm tweaking a single recipe. If you are whipping the butter, you wouldn't fraiser the dough as it could knock any air you added from the whipping process out. Once the dough is formed, I shape it into a disk, wrap it in plastic wrap, and refrigerate it overnight.

Several recipes call for rolling out the dough with flour, but I want to control the amount of flour, so I will roll out the dough between two pieces of parchment paper. First, I whack the dough while it is still inside the plastic wrap with a rolling pin until it is pliable. This is a great way to get your dough pliable while keeping it cool. It is also great stress relief if you are anxious or frustrated.

Then I transfer the dough to two sheets of parchment paper and roll it out to size (~1 in. wider than the tart pan base). When you do this, the dough can warm and stick to the parchment paper, but if you pop it back in the fridge for ~2-5 minutes to harden the butter, the parchment should peel off relatively easily. I've yet to find an elegant solution for getting the dough disk in the tart pan without ripping it, but you can patch any holes (or gaping rips) with the extra dough that hangs over the edges. After the dough is shaped into the pan, you can trim the top by rolling over it with a flat rolling pin. Next I dock the bottom of the crust with a fork to prevent the tart shell from puffing up too much during baking. I then cover the pan in plastic wrap and refrigerate 30 minutes.

For these tests I will fully blind bake the crusts as you would if you were filling the tart with a filling that doesn't need additional baking. After playing around with a few temperatures, 350˚ F seems to be the sweet spot, so I'll use that for all the bakes. The bake time really depends on how thick you roll it out and how pathological your oven is. For the first part of the bake, you want to line the interior with parchment paper and fill it to the top with your favorite weight (pie weights, sugar, rice, beans). This is necessary to keep the side of the tart from melting down into a sad mess. I will take the first part of the bake until the edges are just beginning to brown (~15-20 minutes in my oven). For the second part of the bake, I will take out the parchment paper and weights and bake until the surface in the center of the tart shell is dry and no longer doughy (~2-5 minutes). After baking, I will allow the tart shell to fully cool (~20 minutes) and gently remove it from the tart pan.

Blind baking keeps the tart dough from sinking into the pan in a sad mess like the above shell

Week 1: High Egg Content, High Sugar

This week I am looking into the high egg content and high sugar recipes (Recipes 4 and 5). These recipes have the most flour, presumably to get the right texture with all the liquid from the additional eggs. They also both use a bit of almond flour. The general claim I found in my research is that you can substitute a bit of your flour with almond flour to get the dough texture right without adding additional gluten, which can make the dough tough.

If I were to just bake both of these recipes, it would be hard to learn much since they have different amounts of flour, types of flour, and different types of egg. I need to make the ingredients more uniform and maybe do a few targeted splits based on what I want to learn. It looks like the main questions we can ask here are:

1. Is the difference between cake flour and all purpose (AP) flour noticeable?
2. What is the difference between a whole egg and yolks on the texture?

The doughs are within a gram of sugar, so I'm just going to make them equal. The egg and flour amounts are also very close, so we'll make those uniform too. I also want to add an additional split so we can differentiate between our two questions. My final test recipes are then:

Split A vs. Split B will put cake flour up against AP flour, while Split B vs. Split C will tell us the difference between a whole egg and egg yolks.

Results

Split C is extremely tough compared to Split B, meaning that whole eggs make your dough much tougher. So what is going on here? Egg whites are ~90% water, while yolks are only ~50% water. Additional water results in additional gluten formation when added to flour, so the additional water in the whites toughens the tart shell. Whites are also made up of ~10% protein, which adds additional structure and toughness. Meanwhile, the yolk is made up of ~30% fat, which breaks the gluten down into shorter strands, resulting in a more tender texture. (Side note: This is why they often call fats shortening. Mind. Blown.)

Split A is more tender than Split B. This one is pretty straightforward. Cake flour has less protein content than AP flour. Two proteins in the flour, glutenin and gliadin, develop gluten when added to water, so higher protein leads to more gluten formation, which leads to a tougher texture. Gluten is further developed by working the dough, so this is why all the recipes say to minimize how much we work the dough.

Texturally, Split A is the winner, but the high yolk content also brings an unappetizing metallic flavor to the dough. We've learned some really good information, but none of these high egg content, high sugar content doughs is a winner for me. I am really glad that my husband will eat anything.

Next week we will try out the moderate egg content, low sugar group of recipes, so stay tuned!