Oreo-Chunk Brownies

adapted from Recipe Girl

4 sticks unsalted butter
1 lb semi-sweet chocolate chips
6 ounces unsweetened chocolate, chopped
2 Tablespoons cocoa
7 large eggs
2 Tablespoons pure vanilla extract
2¼ cups granulated sugar
1¼ cups all-purpose flour, divided
1 Tablespoons baking powder
1 teaspoon salt
4 cups broken Oreos (about 40 cookies)

1. Preheat oven to 350°F. Butter and flour 12x18x1-inch pan (Texas sheet cake size). Line with foil or parchment that hangs over the sides for ease in getting them out (butter the foil/parchment).
2. In a heatproof, medium-bowl set over a saucepan of simmering water, heat butter and chocolates until melted and smooth; cool slightly.
3. In a large bowl, whisk together the eggs, cocoa, vanilla and sugar. Stir the egg mixture into the slightly cooled chocolate mixture. Cool to room temperature.
4. In a medium bowl, sift together 1 cup of flour, baking powder, and salt, then add to batter. In a small bowl, stir Oreos and remaining ¼ cup flour. Stir cookies into chocolate mixture. Then pour into prepared baking pan and smooth top with a rubber spatula.
5. Bake for 25 to 35 minutes, or until toothpick inserted in center comes out clean with a few crumbs attached; do not overbake! Let cool completely, then cover tightly and chill overnight. Chilled brownies are easier to cut. Dump the chilled brownie pan onto a large cutting board, peel off the foil and cut into squares.