For the brioche:
In the bowl of a kitchen aid with a paddle attachment, add the flour, sugar, salt, and crumbled yeast. Mix quickly.
Add the eggs and knead for about 2-3 minutes at medium speed, until the dough becomes strong and thick.
Gradually add the diced butter while the mixer is running at medium speed. Knead until the butter is fully incorporated and the dough is dense, smooth, and slightly sticky, about 20 minutes.
Place the dough in a clean bowl, cover with cling film, and let rise in a warm room for about 2 hours, or until it has doubled in size.
Flatten the dough into a rectangle, wrap with cling film, and chill in the refrigerator for about 40 minutes to 2 hours, then freeze for 20 minutes.
For the vanilla custard:
Heat milk and butter on medium heat. Add the vanilla pod and its seeds.
In a separate bowl, whisk the yolks with sugar, flour, and cornstarch until smooth.
Gradually add the hot milk to the egg mixture, whisking continuously.
Return the mixture to the pan and cook on low-medium heat, whisking until thickened.
Transfer to a clean bowl, cover with cling film touching the surface, and refrigerate.
For assembly:
Roll out the dough on a parchment-lined surface into an 8×12 inch rectangle.
Spread the custard over half of the dough, then sprinkle with chocolate chips.
Fold the dough over, cut into 8 rectangles, and let rise on a baking sheet for 2 hours.
Bake at 350°F (180°C) for 10-12 minutes, then brush with syrup made from sugar and water.