Preheat the oven to 350°F. Lightly grease a 9x11-inch baking dish, 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 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.