Preheat oven to 350 degrees Fahrenheit. Line a muffin pan with paper muffin cups and set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the flour, granulated sugar, vanilla sugar, margarine, and oil until a crumbly mixture is formed. Remove one and a half cups and set aside. (Leave the rest in the mixer bowl.)

To the mixer bowl, add the eggs, orange juice, and baking powder and beat until smooth and fluffy. Remove about 3/4 of the batter and set aside.

Add the cocoa powder to the remaining 1/4 of the batter and beat to combine.

Fill each muffin cup of the way with the light-colored batter (from step 3). Top with one tablespoon brown batter (from step 4) and use a toothpick to gently swirl it in.

Top each muffin with some of the crumbs you set aside in step 2.

Bake for 22–24 minutes, until a toothpick inserted in the center comes out clean.