In the bowl of a mixer with a paddle attachment, add the flour, sugar, salt, and crumbled yeast; mix quickly to combine.

Add the eggs and knead for about 2-3 minutes at medium speed until the dough becomes strong and thick.

Incorporate the diced softened butter in several additions while the mixer is running at medium speed, kneading until the butter is completely 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 doubled in size.

Flatten the dough into a thick rectangle, wrap with cling film, and refrigerate for about 40 minutes or up to 2 hours; alternatively, freeze for 20 minutes.

For the vanilla custard, heat milk and butter on medium heat; add the vanilla pod and grated seeds.

In a separate bowl, whisk together the yolks and sugar, then add flour and cornstarch, whisking until well combined.

When the milk is bubbling, remove the vanilla pod and pour milk over the egg mixture in parts, whisking until well combined.

Pour the mixture back into the pan on low-medium heat, whisking continuously until thickened.

Transfer into a clean bowl, cover with cling film, making contact with the custard, and refrigerate until ready to use.

Remove the dough from the refrigerator and roll it out on parchment paper into a large rectangle of 8x12 inches (40x30 cm).

Cover half of the dough with the custard lengthwise, sprinkle chocolate chips over, and gently press with a rolling pin to make contact with the custard.

Fold the empty side of the dough over the filled side, flattening to remove air bubbles and ensuring a smooth surface.

Cut the dough into 8 equal rectangles, about 1 to 1.5 inches (3 to 4 cm) wide, and place on a baking sheet lined with parchment paper, leaving space in between.

Cover with cling film and let rise for 2 hours.

For the syrup, in a small saucepan, bring sugar and water to a boil until sugar is completely dissolved; let cool.

Brush the risen brioches with the beaten egg and yolk, bake in a preheated oven at 350?F (180?C) for 10-12 minutes or until golden brown.

Remove from the oven and brush with the syrup immediately; let cool completely before serving.