Preheat your oven to 325˚F. Butter and line a 9-inch baking tin.
In the bowl of a stand mixer or using an electric hand mixer, beat together the butter, oil and sugar until light in color, about 3 minutes. Beat in the eggs and vanilla.
In a medium sized bowl, sieve together the flour, cocoa powder, salt and baking powder.
Slowly and carefully add the dry ingredients to the wet ingredients and mix just until the ingredients are evenly combined. Pour half of the batter into your baking tin. Drizzle the caramel all over the batter. Pour in the remaining half of brownie batter, carefully spreading it so you completely cover the caramel. Bake in the oven for 20-25 minutes, or until a toothpick inserted comes out clean.
Cool the brownie in the baking tin for at least 15 minutes and then lift out and leave to cool on a wire rack.