Start by preparing the brioche dough. Put all the dry ingredients in a bowl. Add eggs and mix. Add the milk and mix until having a smooth paste. Finally, add the soft butter, diced and knead until the butter is well absorbed by the dough. Let stand at least an hour. The dough should double in volume.
Just after, prepare the pastry cream. Heat the milk with the vanilla extract. Blanch the egg yolks with the sugar then add cornstarch and mix. Once the milk is hot, pour half the mixture into egg-sugar-cornstarch, stir and pour into the pan with the remaining milk. Heat over medium heat while stirring until it thickens. Then cool to room temperature then refrigerate.
Degas the dough then also stored in the refrigerator for 1 hour.
Store whips, the bowl and cream in the freezer 15 to 30 minutes.
Beat butter and mix with pastry cream. Assemble the cream and gradually add into the pastry cream to obtain a muslin cream.
Take the dough, knead it and then give it the shape you want. You can form a pie, forming a circle of diameter 25cm, or, like me, make small diameter 7cm balls and place them next to each other to make a crown. Leave to swell further 45min at least. After this time, milk spread on it with a brush and add sugar grain. Bake 20 minutes at 180 ° C.
Leave to cool before cutting in length. Remove the top of the crown, spread the cream muslin inside. Replace the top and sprinkle with icing sugar.