Make the custard: In a saucepan, heat milk and vanilla until simmering. In a bowl, whisk egg yolks, sugar, and cornstarch. Slowly pour hot milk into the egg mixture, whisking constantly. Return to saucepan and cook until thickened. Stir in butter, cover with plastic wrap (touching the surface), and chill.

Make the dough: In a stand mixer, combine flour, sugar, salt, and yeast. Add warm milk and eggs. Knead with a dough hook for 5 minutes. Gradually add softened butter, one cube at a time, until fully incorporated and dough is smooth and elastic.

First rise: Place dough in a greased bowl, cover, and let rise in a warm place for 1.5 to 2 hours, or until doubled in size.

Punch down the dough and roll it out on a floured surface into a large rectangle (about 12x16 inches).

Spread the chilled vanilla custard over the bottom half of the rectangle.

Sprinkle mini chocolate chips evenly over the custard.

Fold the top half of the dough over the filling. Gently press down to seal.

Cut the dough into 10-12 equal strips (about 1.5 inches wide).

Place the strips on a parchment-lined baking sheet. Cover and let rise for another 45-60 minutes.

Preheat oven to 350°F (180°C). Brush the brioches with egg wash (egg beaten with milk).

Bake for 12-15 minutes until golden brown.

While still warm, brush the brioches with warmed apricot jam or simple syrup for a professional glossy finish.

Transfer to a wire rack to cool slightly before serving.

Best enjoyed fresh and warm!