Add eggs, warm milk, and vanilla. Mix until a rough dough forms.

Add softened butter a little at a time and knead until the dough is smooth and soft.

Place dough in a greased bowl, cover, and let rise for 1 to 1 1/2 hours, or until doubled.

Melt chocolate and butter together. Stir in powdered sugar, cocoa powder, cinnamon if using, and salt. Let cool until spreadable.

Roll dough into a large rectangle on a lightly floured surface.

Spread chocolate filling evenly over the dough.

Roll tightly into a log from the long side.

Slice the log in half lengthwise.

Twist the two halves together with the cut sides facing upward.

Place the twisted loaf into a greased 9x5-inch loaf pan.

Cover and let rise for 30 to 45 minutes.

Preheat oven to 350°F.

Bake for 35 to 40 minutes, or until golden brown and cooked through.

While baking, simmer sugar and water for 2 to 3 minutes to make syrup.

Brush syrup over the hot babka.

Cool before slicing.