1 cup unsalted butter melted and cooled ▢2 tablespoons vegetable oil ▢1¼ cups granulated sugar ▢1 cup packed light brown sugar ▢4 eggs room temperature ▢1 tablespoon vanilla extract ▢1 cup all-purpose flour ▢1 cup unsweetened cocoa powder ▢¾ teaspoon salt ▢½ teaspoon baking powder ▢1 cup chocolate chips milk or semisweet, divided Toppings ▢sprinkles, toffee bits, crushed Oreos, crushed candies, chopped nuts optional
Preheat the oven to 350°F. Lightly grease a 9-x-11-inch baking dish and line it with parchment paper and set aside. In a medium bowl, combine melted butter, oil, and both sugars and whisk well.
Add eggs and vanilla and mix for another 2 minutes. In another bowl, sift together flour, cocoa, salt, and baking powder.
Fold dry ingredients into wet ingredients and stir until just combined. Fold in ¾ cup chocolate chips.
Pour batter into the prepared baking dish and smooth out until even. Top with remaining ¼ cup chocolate chips and any other desired toppings and bake for 25–30 minutes, or until the middle no longer jiggles.
Let sit in the pan for 10–15 minutes, then remove from the pan and let cool completely before cutting.