brownie pillow cookies

Ingredients:

1 package brownie mix

1 cup butter, room temperature
1 1/2 cups packed light brown sugar
2 large eggs, plus 1 egg yolk
1 tablespoon vanilla
2 1/2 cups all purpose flour
2 teaspoons baking powder
1/2 teaspoon salt
1/2 teaspoon baking soda
12 oz. bag miniature semi-sweet chocolate chips

courtesy of bakerella.com