Brioche : In a bowl, put the flour, the salt, the sugar, and dig a hole. Put the yeast in the middle, being careful it doesn't touch the salt. Add the eggs and the milk, and start to knead at speed 2 for 4 minutes.
Then, while kneading, add the softened butter little by little. Once you add all the butter, keep kneading for 10 minutes. Put in the fridge for 90 minutes.
Vanilla custard : Put the milk to boil with the sliced vanilla bean and its seeds.Meanwhile, put the yolks in a bowl with the sugar. Beat it energetically, until the mix gets creamy.
Add the cornstarch and mix well. Once the milk has boiled, add it gradually to the previous mix. Then put everything back in the pot, and put it back on a medium heat.
Stir constantly with a wooden spoon, until the cream thickens, as it is wanted. This lasts around 10 minutes. Then leave it to cool down.
Take the dough out of the fridge. Roll it out on some flour, and form a 12x15 inches rectangle (30 x 40 cm)
Spread the cold vanilla custard on it, with a margin. Then sprinkle the chocolate chips.
Roll the dough, then cut slices 1.5 inches thick.
Arrange these slices in a round greased mold. Leave to swell 1 hour at room temperature.