Custard:
Put the flour in a bowl, make a volcano and pour the sugar, yeast, and 4 tbsp of warm milk in the center. Allow it to rest for about 10 minutes.
While you wait for the yeast to activate, melt the butter and mix with the rest of the milk.
Put the melted butter and salt over the flour and stir with a wooden spoon until it is easy to manage by hand. Once it is semi-compact, move to the table and knead for about 8 minutes. Put back in the bowl and let it rise for an hour or until it doubles its size.
For the jam, put the blackberries and sugar in a pot, boil over medium heat and wait until the mixture thickens for about 10-15 minutes. Allow to cool.
For the custard, mix the ingredients in a pot, and once all the cornstarch lumps are dissolved, put over medium heat stirring constantly. Once the mixture starts to boil, keep stirring for 2 minutes and remove from the heat. Allow to cool.
Roll out the dough until getting a 23×14 inch rectangle, approximately. Spread ¾ of the custard and blackberry jam, roll carefully so the filling will not come out, split in half, and braid as a donut.
Bake for 30 to 40 minutes in an oven preheated over 350°F or until the crown starts getting golden. Allow to cool over a baking rack.
Once cold, decorate with a pastry bag making custard pompons and sprinkle powdered sugar.
