Preheat oven to 350°F (180°C) or 320°F (160°C fan), spray a 9x13 inch metal pan with oil, and line with parchment paper.
Whisk flour, baking powder, baking soda, and salt together in a large bowl.
In another bowl, whisk egg, milk, sour cream, and olive oil until smooth.
Pour the wet mix into the dry ingredients, stir gently, then fold in the cheese until just combined.
Spread the batter evenly in the pan, top with pizza sauce, shredded cheese, onion, bell pepper, olives, and pepperoni.
Bake uncovered for 25 minutes, cover loosely with foil, then bake another 15 minutes until golden and cooked through.
Cool in the pan for 10 minutes, lift onto a rack, cool another 10 minutes, then slice and serve.