Scale

Cookie dough:

6 tablespoons unsalted butter (melted)

1/3 cup brown sugar

1/4 cup granulated sugar

1 egg

1 teaspoon vanilla extract

1 cup flour

1 tablespoon cornstarch

1/2 teaspoon baking soda

1/4 teaspoon salt

1 cup chocolate chunks or chips

Brownie batter:

1/2 cup unsalted butter (melted)

1/2 cup brown sugar

1/2 cup granulated sugar

2 eggs

1 teaspoon vanilla extract

1/2 cup flour

1/2 cup cocoa powder

1/4 teaspoon salt

1 cup chocolate chunks or chips

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Make the cookie dough:Whisk melted butter with brown and granulated sugar until smooth. Add egg and vanilla, then stir in flour, cornstarch, baking soda, salt, and chocolate chips. Set aside.
Prepare the brownie batter:Mix melted butter with both sugars, add eggs and vanilla. Stir in flour, cocoa powder, salt, and chocolate chunks until combined.
Assemble:Line an 8×8-inch pan with parchment. Spread half the brownie batter, top with half the cookie dough, then repeat. Sprinkle extra chocolate on top if desired.
Bake:Bake at 350°F (175°C) for 30–40 minutes, until a toothpick inserted comes out with moist crumbs. Cool for at least 1 hour before slicing.

For a flavor twist, add nuts, caramel, or espresso powder. Store in an airtight container for up to 3 days or freeze for longer storage.