- Mix bread flour, sugar, salt, and yeast in a large bowl. Add the egg and warm milk, then knead until a dough forms. 
- Incorporate the room temperature butter into the dough and knead until smooth. Cover and let rise for about 1 hour, or until doubled in size. 
- While the dough is rising, prepare the custard cream. Whisk egg yolks and sugar in a bowl until pale. Add flour and mix until smooth. 
- In a saucepan, heat the milk until just boiling, then slowly pour it into the egg mixture, whisking constantly.   
- Return the mixture to the pan and cook over low heat until thickened. 
- Remove from heat and stir in butter, salt, and vanilla essence. Let it cool. 
- Once the dough has risen, punch it down and divide it into 8 equal pieces.  
- Shape each piece into a ball and place on a baking sheet. Cover and let rise again for 30 minutes. 
- Heat oil in a deep fryer or pot to 350°F (175°C). Fry the donuts in batches until golden brown, about 2-3 minutes per side. Drain on paper towels. 
- Once cooled, fill each donut with custard cream using a piping bag. 
- Dust with powdered sugar or roll in granulated sugar (optional). Enjoy!