I always have to suppress an eye-roll when people talk about baking as chemistry. It's not real chemistry. I mean, some of the more avant guard pastry may be, and there are chemical reactions involved in baking, but most home baking is a matter of approximate ratios of flour/sometimes sugar/butter/salt/sometimes egg. You don't have to level off every cup and teaspoon perfectly... eyeballing it works in most cases. You might start off with a quick bread and end up with a cake, but that's because they're not that different... muffins are just an excuse to eat cake for breakfast. That said, it is possible to throw off your ratios inadvertently -- like forgetting to reduce one ingredient when halving a recipe or accidentally grabbing the 1/3 cup instead of the 1/2 cup -- and it change the texture quite a bit. Still edible, but not quite right.
In the case of these particular cookies, there is a certain point where the batter is basically a soft chocolate mousse... a really, really good chocolate mousse with caramel notes of browned butter, earthy cocoa and espresso and just the right amount of cinnamon. If you eat enough of the dough at this stage you can actually throw off your ratios significantly, rendering the final dough too dry and unfit for anything but a cookie crumb crust base. It, um, happened to someone I know...
Recipe: Whole-Wheat Mexican Chocolate Cookies
These cookies are very thin with a delicate crumb, in part because of the pastry flour. I've only managed to reduce the butter by 25%, but since they're so thin you get a lot of cookies and each one packs a pretty satisfying chocolaty punch. Sometimes I roll them thicker ~1/4” if I want something sturdier to make sandwich cookies. You can omit the sesame and cinnamon for a more basic chocolate cookie flavor, or add 1/8 tsp cayenne for a hint of heat.
1 cup whole-wheat flour
1 cup whole-wheat pastry flour
1/2 tsp kosher salt
1/2 tsp baking soda
2 tsp sesame seeds
8 oz. (16 Tbs/2 sticks) cold butter (divided use)
1/2 cup cocoa powder
2 tsp ground cinnamon
1 tsp espresso powder
1 cup sugar
2 egg yolks
1 Tbs vanilla
Combine first five dry ingredients and set aside. Brown 4 Tbs butter in a small skillet until golden brown and fragrant. Pour into bowl of your standing mixer and add cocoa, cinnamon and espresso. Turn on low speed and stream sugar into running mixer. [This helps cool it a little so you don't melt the rest of the butter.] Once sugar is fully incorporated, slice remaining butter into large pats and add to somewhat cooled mixture. Increase speed to high and beat until creamed… 2-3 minutes. The color will go from almost black to a rich brown like chocolate frosting. Reduce speed to medium and add eggs yolks, then vanilla. Beat until batter is nice and thick.
Now you’re just a few eggs and some refrigerator time shy of a mousse. DO NOT EAT MORE THAN A SPOONFUL OF THIS LOVELY BATTER OR YOU’LL RUIN YOUR COOKIES! Add the flour mixture, ½ cup at a time and waiting until flour is mostly incorporated before adding next scoop. Divide dough roughly in half and dump into Ziploc bags or wrap in plastic wrap before flattening into disks. Chill dough for 15 minutes, refrigerate for up to 3 days, or freeze indefinitely [Allow to come to a cool room temp before rolling out]. If chilling, turn on oven to 350F so it'll be ready when you are.
Unwrap dough and place on parchment paper, keeping plastic wrap spread over top. Roll dough to 1/8” thick, remove plastic, and cut into desired shapes. Using an offset spatula or a thin pancake spatula, move shapes to parchment-lined baking sheet and bake 8-10 minutes. Once done, slide cookies, parchment and all, onto cooling rack. Allow to cool completely before removing from parchment.