Activate Yeast: Mix 1/2 cup lukewarm whole milk with 2 tablespoons sugar. Sprinkle 2 teaspoons active dry yeast on top and let sit for about 5 minutes until frothy.

Prepare Dough: In a stand mixer, combine 4 cups flour and 1 teaspoon salt. Add activated yeast mixture, 2 eggs, 1/2 cup melted butter, and 1 teaspoon vanilla. Mix until combined, then knead for 10-15 minutes.

First Rise: Shape dough into a ball, place in a greased bowl, cover, and let rise in a warm spot until doubled, about 1 to 1.5 hours.

Make Filling: While dough rises, mix 1 cup chocolate chips, 1/4 cup cocoa powder, 1/4 cup sugar, 1/4 cup melted butter, and a pinch of salt in a double boiler until melted and smooth.

Shape Dough: Roll risen dough into a 12x18 inch rectangle on a floured surface. Spread cooled filling over the dough, leaving a small border.

Braid Dough: Roll the dough into a log and slice in half lengthwise to expose filling. Twist halves and place in a greased loaf pan.

Second Rise: Cover dough with plastic wrap and let rise for 45-60 minutes until puffed.

Preheat Oven: Preheat oven to 350°F (175°C). Beat 1 egg with milk for egg wash, brush over dough.

Bake: Bake for 30-35 minutes until golden brown.

Cool: Let the babka cool in the pan for 10 minutes before transferring to a wire rack.