1. First, prepare the dough for the donuts by heating the milk in the microwave until lukewarm. Pour the milk into a large bowl with the yeast and add the oil and sugar. Mix well, then add the flour and salt, mixing until incorporated. 2. A rather runny dough will form. Use a mixer to knead for about 10 minutes at medium speed. Pour it into a buttered dish and cover with a damp cloth. Let it rest for about 30 to 60 minutes; it should double in size.
3. Transfer the dough to a lightly floured surface and stretch it with your hands. Cut into circles using a mold. Heat enough oil and fry the doughnuts. It only takes a few minutes for the dough to cook.
4. For the filling, beat the eggs in a medium bowl, add the cornstarch and icing sugar, and mix until smooth. Add the hot milk to the mixture and stir until incorporated.
5. Bring the mixture to a boil, stirring constantly. Once the mixture thickens, remove from the heat and continue stirring. Add La Villita margarine and vanilla extract.
6. Fill the doughnuts with a thin bag and sprinkle with powdered sugar for the finishing touch.
7. Enjoy.