Closely adapted from Alice Medrich To make this recipe you will need to make chocolate wafers and then sandwich them with a chocolate mint filling. Filling options will be addressed at the end of the wafer recipe.
Ingredients
For the Chocolate Wafers 3.0
1½ cup (6.75 oz) AP flour
¾ cup (2.4 oz) unsweetened cocoa powder
1 cup + 2 T (7.875 oz) sugar
¼ t salt
¼ t baking soda
14 T (1¾ sticks) unsalted butter, slightly softened
3 T whole milk (I used ½ T cream plus 2½ T 1%)
1 t vanilla
For assembling the mint sandwiches:
chocolate wafer cookies (from above)
peppermint oil, to taste (start with a few drops only; I find that white chocolate can take more peppermint)
8 oz finely chopped chocolate, bittersweet or white chocolate
2 T unsalted butter, optional (my house is cool--the cookies made without the butter are undeniably crunchier as the chocolate filling is much harder)
Instructions
Place flour, cocoa, sugar, salt, and baking soda in a food processor and process for a few seconds to blend thoroughly and remove any lumps from the cocoa. Cut the butter into chunks and add it to the processor. Pulse several times. Combine the milk and vanilla, and then pour it into the processor while the blade is running. Process until the dough clumps around the blade or the sides of the bowl. Transfer the dough to a clean surface and knead briefly, much as you would scone dough, to make sure it is evenly mixed. (I doubled this recipe, which was difficult in my processor, so after processing briefly, I finished the mixing by more extensive kneading, which worked fine).
Form the dough into a log approximately 14 inches long and 1¾ inches in diameter. Wrap the log in plastic wrap and then place in a paper towel roll that has been sliced lengthwise (this last step is not necessary but it will help you to get rounder slices). Place in the fridge to chill until firm, a minimum of 1 hour and up to 3 days (I chilled overnight).
Preheat the oven to 350 F. I chose to only bake 1 sheet at a time on a center rack, but if you do 2 be sure to place the racks in the upper and lower thirds of the oven. Line a cookie sheet with parchment paper. Slice the cookies extremely thin, about ⅙-inch (for wafer cookies that will not be sandwiches, slice them a scant ¼-inch), and place them on the prepared cookie sheet, 1 inch apart (I baked 20 per sheet). Bake for 12-15 minutes (be sure to rotate halfway if doing 2 sheets); the cookies will puff and then deflate; Medrich notes they are done about 1½ minutes after deflating but I never managed to confirm this. Mine were done at 15 minutes--she does say if the cookies are at all chewy to bake them for additional time, otherwise they will not crisp properly.
For assembling the cookies: Melt the chocolate and butter (if using) in 30 second intervals in the microwave at 50% power until it can be stirred smooth. Add the peppermint oil to taste--the cookies I made with bittersweet chocolate were less minty and much more chocolatey. The white chocolate I made quite minty. Remember when adding it that the cookies have no mint at all.
Using a ½ teaspoon, dollop a small amount of mint chocolate onto the top of one cookie. Use the bottom of the spoon to spread it nearly to the edges of the cookie, but not quite (see photos). Place another cookie of similar size, top-side-up, onto the filling and press together. Set aside to set completely before storing.
Recipe by The Spiced Life at https://www.thespicedlife.com/chocolate-mint-sandwiches/