Make the starter by dissolving the yeast in the milk. Add the sugar, stir, then add both flours. Knead to form a ball, cover with plastic wrap, and let rise for about 2 hours.

Take the risen starter and dissolve it in the warm milk.

Add the lightly beaten egg yolks, honey, sugar, vanilla, and flour a little at a time, mixing until you get a smooth dough.

Spread the dough out on your work surface and add the softened butter in pieces. Knead until fully incorporated, then add the chocolate chips.

Gently score the top with a sharp blade to make a cross. Place a few small pieces of butter in the cuts and bake at 350°F (180°C) for about 45 minutes.

Cover with aluminum foil if it starts to brown too much.