Carnival doughnuts with blueberries

Making the blueberry puree
Pour the blueberries in a saucepan, add the sugar and leave to break down on a low heat.

Making the doughnuts
Mix the milk, yeast and a soupspoon of the sugar. Set aside for 10 minutes. Add the flour, remaining sugar and salt flakes and blend thoroughly. Add the eggs and vanilla, then gradually the butter. Once this mixture is fully combined, blend for about 10 minutes. The dough is ready when it comes off the side of the bowl.
Transfer the dough to a large bowl, and leave to rest (for about 90 minutes) until it doubles in size. 
Cut fifteen 4 x 4cm pieces of paper and prepare two large baking trays. Knead the dough briefly to remove air bubbles, then cut into 15 portions (55g each). Roll the portions into balls, flatten slightly, then place on a sheet of baking paper. Leave to double in size for 1 hour.
Heat the oil to 170°C (340°F). Fry each side for 90-120 seconds. Place the doughnuts on absorbent paper, then roll in sugar.

Making the pastry cream
Whisk the egg yolks and sugar until the mixture turns pale. Add the flour and blend thoroughly. Add half a glass of milk to make the mixture more liquid, and blend well. Heat the rest of the milk until it briefly boils, then pour onto the mixture of eggs, flour, sugar and milk. Blend thoroughly, then pour into the saucepan. Add the split vanilla pod and the seeds, having scraped them out. Whisk until the mixture comes to the boil.
Remove from the heat, leave to cool slightly, then add the blueberry puree and blend well. (NB: do this at the last moment, as the blueberry pastry cream will quickly turn black).
Transfer into a piping bag fitted with a round tip. Reserve in the fridge.

Filling the doughnuts
Using the piping bag, fill each doughnut with blueberry pastry cream.

Thanks : 

Recipe made by Stéphanie Iguna (Stephatable).