Preheat oven to 325 degrees F. Melt the butter and unsweetened chocolate over low heat in a medium saucepan, stirring constantly. Remove from heat; cool slightly.

Stir the sugar into the cooled chocolate mixture in saucepan. Add the eggs, one at a time, beating with a wooden spoon just until combined. Stir in the vanilla.

Stir together the flour and baking soda in a small mixing bowl. Add the flour mixture to the chocolate mixture; stir just until combined. Press one-half of the cookie dough into an 8x8-inch Reynolds® Bakeware Pan. Spread brownie batter evenly over cookie dough. Crumble remaining cookie dough and sprinkle evenly over brownie batter. Press down slightly.

Bake 50 to 55 minutes or until edges are firm are starting to pull away from sides of the pan. Cool on a wire rack. Cut into bars.