Preheat your oven to 350°F (175°C) and line a 9x13 inch baking pan with parchment paper.

Melt the butter in a medium saucepan then transfer to a mixing bowl. Whisk in the vegetable oil, granulated sugar, and brown sugar until blended. Add eggs one at a time with vanilla extract.

In a separate bowl, whisk together the cocoa powder, flour, and salt.

Gradually mix dry ingredients into wet ingredients, being careful not to overmix. Fold in chopped Oreos.

Pour the batter into the prepared pan and bake for 25-30 minutes. Check for doneness with a toothpick.

Cool the brownies in the pan for 1.5 hours before transferring to a wire rack.

Optionally, prepare frosting by beating softened butter, then gradually add powdered sugar, vanilla extract, and heavy cream.

Decorate with leftover Oreos and sprinkles using frosting as glue.

Spread frosting on cooled brownies, top with decorated Oreos, and serve cut into squares.