This is an easy recipe for big, chocolatey American muffins that can be made without butter. Mix sugar and eggs together, then sift in cake flour, bread flour, cocoa powder, and baking powder. Add milk and oil and mix gently. Mix crushed Oreos into the batter, pour generously into muffin cups, smooth the surface, and top with crumble and Oreos. Bake in a 180°C oven, and you'll have satisfying chocolate muffins that are crispy on the outside and fluffy on the inside.