01 -
1 cup unsalted butter, softened (for cookies).
02 -
3/4 cup granulated sugar.
03 -
3/4 cup dark brown sugar.
04 -
1 egg.
05 -
1 2/3 cups all-purpose flour.
06 -
2/3 cup cocoa powder.
07 -
1 teaspoon salt.
08 -
1/2 teaspoon baking soda.
09 -
3/4 cup unsalted butter, softened (for filling).
10 -
2 cups confectioners' sugar.
11 -
1 tablespoon milk.
12 -
1/2 teaspoon vanilla extract.
13 -
1/2 teaspoon kosher salt (for filling).