Preheat oven to 350°F (175°C) and grease an 9×13-inch pan thoroughly
Cream butter with light brown sugar in a bowl until smooth for 3 minutes
Beat in 2 eggs, 1 tsp vanilla extract, and 1 tbsp melted butter
Sift 2 cups flour with baking soda and salt, then gradually mix into the bowl
Reserve half the cookie dough; press the base layer into the pan
Bake cookie dough for 15 minutes; let cool slightly
Crush 20 Oreos into pieces, mix with 1/4 cup melted butter, and spread evenly over cooled base
Melt 1 cup (halal-certified) butter or coconut oil with 6 oz dark chocolate over low heat
Whisk in 1 cup granulated sugar, 2 eggs, and 1/2 cup cocoa powder
Add 1 tsp baking powder and remaining 1 1/4 cups flour plus 1/4 tsp salt
Pour brownie batter over the Oreo layer
Bake the stacked layers for 18-20 minutes until a toothpick inserted in the center comes out with moist crumbs
Let cool completely in the pan before cutting into 24 squares