- 1 cup (2 sticks) unsalted butter, cut into small pieces, plus more for pan
- 1 cup all-purpose flour, plus more for pan
- 10 ounces semisweet chocolate, coarsely chopped
- 1 cup (about 4 1/2 ounces) malted-milk powder
- 1 cup (about 4 ounces) malt balls, coarsely crushed
- 1 1/2 cups packed light-brown sugar
- 3 large eggs
- 1 tablespoon pure vanilla extract
Preheat oven to 350 degrees. Butter and lightly flour a 9-by-13-inch baking pan; set aside. Combine chocolate and butter in a heatproof bowl set over simmering water; stir until melted and smooth. Set aside to cool slightly, about 5 minutes.
In a medium bowl, whisk together the flour, malted-milk powder, and malt balls; set aside. In the bowl of an electric mixer fitted with the whisk attachment, beat sugar and eggs until thickened and fluffy, about 2 minutes. Add melted chocolate mixture and vanilla; mix to combine, about 30 seconds more. Using a spatula, fold in flour mixture until just combined.
Pour batter into prepared pan, spreading it evenly with a rubber spatula. Bake until a cake tester inserted in the center comes out with just a few crumbs on it, 30 to 35 minutes. Transfer brownies to a wire rack to cool.