Uncle Drew's Skillet Brownies

Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9-inch oven-proof skillet. Place butter in a microwave-safe bowl; heat in microwave until melted, about 30 seconds. Add sugar and cocoa powder to butter and stir. Heat butter-cocoa mixture in microwave until sugar is dissolved and mixture is smooth, about 30 seconds. Mix vanilla extract into butter-cocoa mixture. Stir eggs into butter-cocoa mixture; add flour and stir until batter is well mixed. Pour batter into the prepared skillet. Bake in the preheated oven until a toothpick inserted in the center of the brownies comes out clean, 40 to 50 minutes.