Very soft variegated donut

Very soft variegated donut
Ingredients
For the dough:

4 eggs
200 g sugar
100 ml seed oil
150 ml milk
300 g 00 flour
1 sachet baking powder (16 g)
1 teaspoon vanilla extract or grated zest of a lemon
30 g bitter cocoa powder
To decorate:

Powdered sugar