Cream the butter and sugar together until soft.
Mix the yeast with the warm water and a pinch of sugar and put this to one side.
Beat the eggs together.
Sift the flour and salt into the bowl of a food mixer and make sure that the dough hook attachment is fitted.
Turn the mixer on to medium and add the yeasted water and the eggs to the dry ingredients.
When the dough has started to bind together, start to add the creamed butter and sugar in small batches, continue to beat with the dough hook.
When it is all mixed together and the dough comes away from the sides of the bowl, place it somewhere warm to prove for two hours.
After two hours, knock the air out of the dough, wrap it in clingfilm and place it in the fridge for at least 12 hours or overnight.
**NOW MAKE THE PASTRY CREAM**
Split the vanilla bean lengthways and scrape out the seeds.
Combine the milk, butter, vanilla bean and seeds in a saucepan and bring to a boil.
Whisk the egg yolks with the sugar in a bowl until the sugar is mixed in and the mixture is quite pale. Then add the corn flour and flour.
Strain the hot milk into the egg mixture, whisking constantly.
Return the mixture to the saucepan and stir until the cream thickens.
Remove the pan from the heat and scrape the pastry cream into a shallow bowl. Place a piece of clingfilm on the surface of the pastry cream to stop it forming a skin, then chill it completely.
**BACK TO THE BRIOCHE**
The next day, roll the dough out to a rectangle 4mm thick, you must work quickly, the moment the dough begins to warm up, it will be hard to work with.
Cover half the dough in creme patissiere and chocolate chips, fold the other half of the dough over the top, cut the brioche into slices around 3cm wide.
Leave to prove somewhere warm for two hours, until almost doubled in size.
Then glaze with egg wash and then bake for 15mins at 200 degrees C, until they are golden.