Dough: Mix yeast with a few tablespoons of warm water and a pinch of sugar, set aside for about 10-15 minutes (by then the yeast should be foamy). Sift flour into a large bowl, add the yeast dissolved in water, sugar, salt, and 3 eggs. Mix the ingredients with a wooden spoon. Gradually add the remaining 2 eggs while working the dough by hand. Work for about 10 minutes until the dough is smooth and elastic. You can also use a mixer with a special dough hook for yeast dough, initially at low speed, then increase to medium speed.
Gradually add butter, 2 tablespoons at a time, mixing or mixing with a mixer. Add the next 2 tablespoons of butter quickly, as soon as the previous portion blends in with the dough. Cover the bowl with transparent film and set aside in a warm place without drafts until it doubles in volume, about 1 and 1/2 to 2 hours. Punch the dough with your fist, cover again, and place in the refrigerator overnight.
Cream: Heat the milk in a saucepan. In a plastic bowl, beat egg yolks with sugar using a mixer, then blend with cornstarch. Gradually pour in the hot milk while mixing constantly. Pour into the saucepan and bring to a boil. Cook over medium heat for about 2 minutes, stirring constantly. Remove from heat, mix in vanilla extract, and pour into a clean bowl. Cover and chill in the refrigerator (for at least 1 hour).
Roll out the dough on a lightly floured surface into a rectangle approximately 30 x 45 cm, thin to 1/2 cm. Spread the cold cream on the surface of the dough, sprinkle with chocolate pieces. Fold the shorter sides of the dough to the center so they meet in the middle, then cut the dough in this place into two parts. Cut each half crosswise into 12 strips. Arrange them on a baking sheet lined with parchment paper, 2 cm apart. Loosely cover with film and set aside to rise for about 1 and 1/2 hours.
Preheat oven to 190°C. Brush the top of the dough lightly with beaten egg. Bake until golden for about 15-20 minutes. Cool on a baking sheet placed on a metal rack.
