Melt semisweet and milk chocolate gently to make chocolate-covered toffee.

Toss about 1/2 cup of homemade toffee pieces in the melted chocolate until coated.

Spread on parchment, let harden, then chop into 1/2-inch pieces.

Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.

Whisk together all-purpose flour, black cocoa powder, baking powder, baking soda, and salt in a medium bowl.

Cream together softened unsalted butter and packed light brown sugar until pale and fluffy.

Add the flour mixture to the butter mixture and fold until just combined. Stir in the chocolate-covered toffee pieces.

Cover the bowl and refrigerate the dough for 30 minutes before baking.