Step 1

In a medium bowl, combine the butter, granulated sugar and brown sugar. Using a hand mixer on low speed, beat the ingredients until light and fluffy but still a bit grainy, about 3 minutes. (If mixing by hand, you’ll see the sugars just beginnng to dissolve into the butter as they’re combined, 4 to 5 minutes.)

Step 2

With the mixer running, add the whole egg and beat (or stir) on low until thoroughly incorporated. Add the yolk and milk and beat (or stir) until thoroughly incorporated. The batter will begin to look smooth and glossy. Beat (or stir) in the vanilla extract until combined.

Step 3

In another medium bowl, whisk together the flour, baking soda and salt until thoroughly combined.

Step 4

Add the flour mixture to the butter and egg mixture and mix on low speed (or stir) just until the flour is incorporated. Using a silicone spatula, scoop to the bottom of the bowl and gently incorporate any hidden pockets of flour.

Step 5

Fold in about 10 ounces of the chocolate wafers (you can eyeball this; just be sure to reserve a handful of wafers to top the dough balls).

Step 6

Spoon the dough onto parchment paper or plastic wrap and wrap it into a disk or log (whatever will fit best in your refrigerator) and refrigerate overnight. If baking the same day, use a tablespoon to portion 2 tablespoons (30 grams/1 ounce) of dough per cookie -- you should get 36 -- and refrigerate until thoroughly chilled, at least 1 hour and up to 3 hours.

Step 7

When ready to bake, position a rack in the upper third of the oven and preheat to 350 degrees. Line a large sheet pan with parchment paper.

Step 8

Transfer the chilled dough to the counter. If the dough was chilled overnight, portion out the cookies as instructed above.

Step 9

Use your hands to roll each cookie into a ball and place on the prepared cookie sheet. Allow about 2 inches of space in between each dough ball.

Step 10

Gently press each dough ball into a thick disk, tuck 2 to 3 chocolate wafers into the top of each dough ball, and sprinkle generously with flaky sea salt, if using.

Step 11

Bake one sheet at a time, for about 12 minutes, rotating the pan front to back after about 7 minutes; the cookies should be golden brown. (If you want crisper edges and deeper color, bake for 1 more minute.)

Step 12

Let the cookies rest on the sheet for 3 minutes, then carefully transfer to a wire rack to cool completely or until warm.