Yield: 6 large sandwiches.

¾ cup unsweetened cocoa powder, sifted
1½ teaspoons kosher salt
1 teaspoon baking powder
2½ cups all-purpose flour, plus more for dusting
2 sticks unsalted butter, room temperature
½ cup light brown sugar
½ cup dark brown sugar
¾ cup granulated sugar
2 large eggs, room temperature
2 teaspoons vanilla
3 pints good-quality ice cream (any flavor)
Sprinkles, chopped nuts, chopped chocolate chips, or colorful cereal (optional)

For the cookie dough: In a medium bowl, whisk together the cocoa powder, salt, baking powder, and 2½ cups flour.
In the bowl of a stand mixer, beat the butter, light and dark brown sugar, and granulated sugar on medium-high speed until light and fluffy. Reduce mixer speed to medium and add eggs one at a time. Add vanilla; beat eggs until fluffy, about 30 seconds. Reduce speed to low and gradually add dry ingredients, beating until just combined and scraping down sides and bottom of bowl with rubber spatula. Divide dough in half and wrap each half in plastic wrap, pressing down to form into ½-inch-thick discs. Chill until firm, at least 4 hours or overnight.

Preheat oven to 350°. Line 2 baking sheets with parchment paper. Remove dough from refrigerator and bring to room temperature for approximately 5 minutes.

Lightly flour countertop and rolling pin. Roll out dough to a ⅛-inch-thick rectangle. Dust dough with more flour as needed. Use a 4-inch round cookie cutter to cut out as many rounds as you can, then use a thin metal spatula to transfer cut dough onto baking sheets, spacing 1 inch apart. You should end up with approximately 12 cookies total.

Chill dough on baking sheets in refrigerator for 10 minutes. Remove baking sheets from refrigerator and bake cookies for 12 to 15 minutes, rotating baking sheets once during baking process. Let cool on baking sheets.

For the ice cream: Line a 9 x 13-inch baking sheet, preferably straight-sided, with 2 layers of plastic wrap, leaving several inches of overhang on all sides; place in freezer. Remove ice cream from containers and place in a large bowl. Let sit until slightly softened, about 5 minutes, then stir with a wooden spoon or a large rubber spatula until the ice cream reaches the consistency of thick cake batter. Scrape ice cream into chilled pan and use a small, offset spatula to smooth into an even layer. Freeze, uncovered, until firm, 15 to 20 minutes.

To assemble: Remove ice cream from freezer, unwrap, and invert onto a cutting board; remove pan and peel off plastic. Working quickly, press 4-inch round cookie cutter straight down into ice cream. Working with 1 round of ice cream at a time, use a thin metal spatula to place it on a flat-side-up cookie and top with a right-side-up cookie. Transfer sandwiches to a rimmed baking sheet set in the freezer as you work. Roll sides of sandwiches in sprinkles, chopped nuts, chopped chocolate chips, or colorful cereal, depending on flavor of ice cream. Freeze sandwiches until ice cream is hard, about 2 hours. Cover sandwiches with plastic wrap and freeze overnight.