Cream fritters: the result is just irresistible!

INGREDIENTS
90 ml (6 tablespoons) warm water
150 ml (⅔ cup) buttermilk ;
1 egg;
50 g (2 tbsp.) melted butter ;
500 g (4 cups) flour ;
50 g (¼ cup) sugar ;
7 g (2 oz) dry yeast ;
pastry cream to fill;
Sugar to cover.

METHOD
Whisk warm water with ⅓ of all the sugar and add dry yeast. Whisk again and let stand for 5 minutes.
Add the leftover sugar, buttermilk, eggs and melted butter to the yeast solution. Whisk until the sugar dissolves.
Combine liquids with flour and knead dough until smooth, about 10 minutes. Transfer to an oiled bowl, cover and let rest for 1 hour.
Roll out the dough and cut it into circles. Use a small round cookie cutter to cut out the middle of half the dough circles.
Spray a little water over the entire round and place circles with the hole in the middle on top. Press down lightly. Let rest for 15 minutes.
Heat vegetable oil to 180C/350F. Fry the doughnuts on both sides for 3-4 minutes. If the center puffs up, make a small slit to let the air out.
Cover the golden donuts with sugar and fill each donut hole with custard.