In a small saucepan, warm 1 cup of milk over low heat until lukewarm, then sprinkle 2 teaspoons of active dry yeast on top and let it bloom for about 5 minutes.

In a large mixing bowl, whisk together 4 cups of all-purpose flour, ½ cup of granulated sugar, and 1 teaspoon of salt.

Mix in the bloomed yeast, 2 eggs, and ½ cup of melted unsalted butter until a sticky dough forms.

Transfer the sticky dough onto a floured surface and knead for about 10 minutes until it's smooth and elastic.

Place the kneaded dough into a greased bowl, covering it with a damp cloth or plastic wrap, and let it rise in a warm area until it doubles in size, about 1 to 1.5 hours.

Melt ½ cup of unsalted butter in a small saucepan over low heat. Stir in ⅓ cup of cocoa powder, ½ cup of sugar, 1 cup of dark chocolate chips, and 1 teaspoon of vanilla extract until you have a smooth chocolate filling.

Punch down the risen dough gently. On a floured surface, roll it into a rectangle approximately 12x16 inches and spread the chocolate filling evenly over the dough.

Roll the dough tightly into a log and, using a sharp knife, cut the log in half lengthwise, exposing the chocolate swirl.

Twist the two halves together, keeping the cut sides facing up, and place into a lined loaf pan. Cover with a cloth and let it rise again for 30 to 45 minutes.

Preheat your oven to 350°F (175°C). After the second rise, brush the top with an egg wash and bake for 40 to 45 minutes, until golden brown.

Let the Chocolate Babka cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely before slicing.