Any Kind of Shortbread Sandwich Cookies

Makes around ~12 2.5" cookies 

Though once you're confident, I recommend doubling the recipe to make all the time and effort worth it!

This recipe is intended an a step zero for learning how to develop your own baking recipes!

I've chosen the sandwich cookie because the basic parts, the shortbread cookie and the filling and both simple recipes, with short ingredient lists and few technical challenges. But are endlessly riffable and quite resiliently delicious despite changes.

By making this recipe, and learning how to tweak it, you'll gain an understanding of what each ingredient does in a baked good, what happens when you change them, what you can change and what needs to stay exactly as written. You can take this foundation (which is less the specific facts, and more a method for how to research and test things), and apply it to any recipe!

Ultimately recipe creation boils down to this:

Research and collect similar recipes. Blend them together to create your best guess of a basic version of what you want. Tweak it to add the flavoring and texture you're looking for. Make it, lament that it's not perfect, research and consider improvements for next time. Repeat till perfect!

Ingredients

For Plain Cookies

88g room temp butter

45g confectioner sugar

1/2 tsp vanilla

1 room temp egg yolks

127g sifted AP or cake flour

A pinch of salt

For Matcha or Hojicha

Add 5g matcha or hojicha powder

For Nuts (my favorite!)

Replace 127g of flour with: 27g nut flour or finely ground nuts 100g AP flour. (Almond, hazelnut, sesame, and walnut have all been tasty in the past)

Add like a big handful of nuts chopped into fine (3/16" or 1/2cm) pieces. The nut pieces are largely for visual appeal, so add as much as you think looks nice (or omit altogether) 

For Cereal Cornflakes 

Replace 127g of flour with: 27g ground up corn flakes 100g AP flour 

A handful of Cristi Tosi's Cereal Crunch, recipe below!

To Make the Cookie

Step 1 : Cream Butter

Cream butter, vanilla, and sugar together until light and fluffy.

This will take ~6 minutes with stand mixer on medium high with the paddle attachment, or 10 with electric hand mixer. You could also try a food processor, but I've never done it myself!

Refer to this video for pointers on how to cream the butter and sugar. You're looking for a very pale yellow that looks smooth and fluffy! Mixing too long or not long enough could make your cookies dense, but for this specific recipe, it's fine to overmix a little

Step 2 : Add Wet Ingredients

Add egg yolks and liquid flavorings (if using) and beat till incorporated

Note: Usually, regardless of what flavor the cookies are, the process and ingredients are the same before adding the dry ingredients. To test out multiple new combinations and flavors at once, I often split the dough in half at this stage and continue each half separately with a different flavor in each. 

Step 3 : Add Dry Ingredients

Add sifted flour, salt, and other dry ingredients (if using) and fold with spatula until just incorporated. 

Do NOT overmix. It would be better if you stopped mixing when you can still see just a few steaks of flour than to overmix. I recommend using a spatula instead of a mixer because it's harder to overmix while doing things manually. 

If you are using mix ins, add them just before the dough in fully incorporated 

Step 4 : Form and Rest

Dough should be easily formable into a soft but solid ball. On a piece of parchment, roughly form the dough into a 2" diameter log, then use the parchment to roll the dough into a perfect cylinder.

You can refer to this video for reference on how to roll the dough into parchment paper to get a nice cylinder of dough!

Rest in fridge at least 2 hours, best results overnight. Resting allows the ingredients to hydrate and meld, deepening the flavor and enhancing the texture. It really makes a difference so be sure you do it!!

Step 5 : Make Filling

Just before baking the cookies, make the filling of your sandwich! There are so many variations that work well here, but it has to be something that is a little hardier in texture so that it can support being sandwiched. For example, you could try...

Buttercream

Ganache

If you'd like something a little wetter, like a jam or a curd, consider also making a stiffer filling to surround and contain the wetter one. Here's a video of what I mean!

Here's a versatile recipe for White Chocolate Ganache that has worked well for me!

Make sure your filling is room temp when you go to fill your cookies! Otherwise it might be too stiff to spread evenly

Step 6 : Bake Cookies

Preheat oven to 350°F

Unwrap the roll of dough. If you'd like, you can roll the log in some stuff to add a nice textural element. Coarse sugars, seeds, nuts, and other nice crunchy things are great here. Beware things that might melt in the oven though!

Using a big kitchen knife, cut the log into 3/16” slices (a ruler helps) and arrange slices on a baking sheet with parchment paper. To keep the shape pretty, keep remaining dough slices in fridge while each batch bakes.

It's somewhat difficult to cut the cookies to even thickness with a knife. Make sure the dough is cold and stiff and that you regularly wipe dough residue off the knife. I think alternatively, instead of shaping the dough as a log in step 4, you could roll the dough into a flat sheet between two parchments, chill it in the same way, and then punch the cookies out as long as you keep the dough cold cold cold. But I've never tried this!

Bake until edges and bottom are every so slightly golden. The center of cookie should still be soft. In our oven it's 5-6 minutes but just watch them like a hawk, they burn easily.

Cool to room temp

Step 7 : Sandwich 'em up!

Pair off the cookies. Try to pair them with a partner cookie that is as similar as possible in size and shape. 

With a small spoon to add a bit of filling to one side of the cookie. You could also do this with a piping bag, but the spoon works great! 

Gently press the partner cookie on top of the filling. The cookies are a bit delicate and break easily so be careful! To prevent cracking, apply even pressure across the whole surface area of the cookie, using both hands. One to support the bottom cookie and the other to slowly press the top one into place. 

Step 8: Enjoy!

You can eat these immediately! Or you can place in fridge up to a few days. Chilling them overnight is great because it softens the cookies slightly and stiffens the cream!