Make Cream: Whisk yolks, sugar, and cornstarch. Pour in hot vanilla milk, return to heat, and whisk until thick. Chill.
Make Dough: Knead flour, milk, cream, yeast, sugar, and salt. Add butter gradually. Knead until elastic (10 mins).
Rise: Let dough rise in a warm spot for 1.5 hours until doubled.
Assemble: Roll dough into a rectangle, spread with cold cream, sprinkle with chocolate chips. Roll up and slice.
Second Rise: Let rolls proof for 45-60 mins on a baking sheet.
Bake: Brush with egg and bake at 200°C (400°F) for 13-15 mins. Glaze with syrup while hot.
