Ingredients
1 cup unbleached all-purpose flour
1/4 cup Dutch-process cocoa powder
1 teaspoon baking powder
1/2 teaspoon kosher salt (we use Diamond Crystal)
6 ounces semisweet chocolate, such as Baker's, chopped (1 1/2 cups)
1/2 cup vegetable shortening, melted
1 teaspoon pure vanilla paste or extract
2 large eggs
2/3 cup packed light-brown sugar
1/3 cup granulated sugar
Flaky sea salt, such as Jacobsen, for sprinkling
2 pints assorted ice cream, such as pistachio, caramel, chocolate, and berry swirl
Preparation
Preheat oven to 350°F, with racks in upper and lower thirds. Line 2 baking sheets with parchment. In a bowl, whisk together flour, cocoa, baking powder, and kosher salt. Melt chocolate in a heatproof bowl set over (but not in) a pot of simmering water, or in the microwave, stirring every 10 seconds.
Stir in shortening and vanilla to combine. Beat eggs with both sugars on medium-high speed until pale, fluffy, and doubled in volume, about 5 minutes. Gently fold in flour and chocolate mixtures, alternating in two additions each, just to combine (do not overmix).
Scoop 1-ounce (2-tablespoon) balls of dough; transfer to prepared sheets, spaced 2 inches apart. Sprinkle tops with flaky salt. Bake, rotating sheets and rack positions halfway through, until cookies spread and dome, with small cracks beginning to form on tops, 8 to 10 minutes. Let cool on sheets on wire racks 5 minutes, then transfer cookies to racks and let cool completely.
Meanwhile, temper ice cream in refrigerator until softened but not melting, about 20 minutes. Sandwich 1/4 cup ice cream between 2 cookies; repeat with remaining ice cream and cookies. Freeze until ice cream is firm, at least 1 hour, then transfer to a freezer bag to store up to 1 week.
