Combine all-purpose flour, sugar, salt, and fresh yeast in a stand mixer. Add eggs and mix on medium speed for about 10 minutes until smooth and elastic.

Gradually incorporate softened unsalted butter, kneading for an additional 15-20 minutes. The dough should be sticky yet elastic.

Cover the dough with plastic wrap or a kitchen towel and place in a warm environment for approximately 2 hours until doubled in size.

Gently heat whole milk and butter over low heat with a split vanilla pod until melted. Whisk egg yolks, sugar, and cornstarch together separately.

Slowly add the warm milk to the egg mixture, whisking continuously. Return to saucepan and cook over medium-low heat until thickened, about 8-10 minutes, then chill.

Once the dough has risen, turn it onto a floured surface, roll it into a rectangle, spread custard, and sprinkle with chocolate chips.

Roll the dough, cut into 8 pieces, and place in a greased baking dish to rise for another 2 hours.

Preheat oven to 350°F (180°C). Brush tops with egg wash and bake for 10-12 minutes until golden brown and puffy.

Create a simple syrup with boiling water and sugar, brush over warm pastries, and cool slightly on a wire rack before serving.