All the ingredients should be right from the fridge! Combine the yeast with milk until dissolved. Combine the flour, sugar, eggs and vanilla in a mixer bowl. Stir until combined, and gradually add the milk with yeast. Stir the mass on a low speed for 5 minutes, and add salt. Increase the speed by an average, and knead for 8 to 10 minutes. Add the butter pieces of in several passes at low speed, mixing well each time. Increase the speed, and knead the dough for 10 more minutes. Check the readiness by stretching the dough in front of the window; it should stretch almost to transparency.
Place the dough in a bowl greased with vegetable oil; tighten it with plastic wrap, and refrigerate for 8 hours (better overnight).
The next day, take it out, and roll it into a ball; cover it with the film or a towel, and leave it on the table for 30 minutes. Roll gently into a 1 cm (0.4 inch) thick layer, and leave for 10 more minutes. Cut off the donuts. Transfer them to the lightly floured paper. Cover it with plastic wrap or a towel, and let it stand for at least 1 hour.
Mix the sugar with cinnamon. Heat the oil to 160-170C (320 to 338F). If there is no thermometer, then throw in a piece of dough in the oil; if it gradually turns golden, then you can fry the donuts. Put the finished donuts on a paper towel, and then roll them in a mixture of sugar and cinnamon. Cool and stuff at your discretion.
For the ganache: heat 100 g (3.55 oz) of cream, and add 150 g (5.30 oz) of milk chocolate; mix well, and whisk. Place it in the fridge.
For the curd: mix 3 yolks, 70 ml (2.40 oz) of lemon juice (you can replace a part with the passionfruit), lemon zest, 90 g (3.15 oz) of sugar, 60 g (2.10 oz) of butter in a saucepan with a thick bottom. Stir constantly, and bring it to a boil; cook for 20 to 30 seconds.