Dough: 3/4 c milk, warned to 105–115°F (40-46ºC)
1/2 c plus 2 t sugar
1 T active dry yeast
14 oz (397 grams) all-purpose flour
2 eggs + 1 egg yolk
1 t vanilla extract
3/4 t salt
10 T unsalted butter, cubed and softened
Egg wash: 1 egg yolk
1 T heavy cream
Chocolate filling: 6 T unsalted butter, softened
4 oz bittersweet chocolate, finely chopped
1/4 c sugar
1. Combine milk and 2 t sugar in bowl of stand mixer. Add yeast and let stand for 5 minutes until foamy.
2. Add 2.5 oz flour to yeast mixture and beat at medium speed until combined.
3. Add eggs and yolk, vanilla, salt, and remaining 1/2 c sugar and beat until combined.
4. Reducing speed to low, mix in remaining flour, a bit at a time.
5. Increase speed to medium, then beat in butter a few pieces at a time. Continue to beat until dough is shiny and forms strands from paddle to bowl, about 4 minutes. (Dough will be very soft and sticky.)
6. Scrape dough into a lightly oiled bowl and cover bowl with plastic wrap. Let dough rise until doubled in bulk, 1 1/2 to 2 hours.
7. Punch down dough with a lightly oiled rubber spatula, then halve dough.
8. Roll out each piece of dough on a well-floured surface with floured rolling pin into an 18” by 10” rectangle.
9. Spread 3 T softened butter on each rectangle of dough, leaving a 1/2-inch border all around. Brush some of egg wash on a long border.
10. Sprinkle half of chocolate evenly over buttered dough, then sprinkle with half of sugar (2 T).
11. Starting with a long side, roll dough into a snug log, pinching firmly along egg-washed seam to seal. Bring ends of log together to form a ring, pinching to seal. Twist entire ring twice to form a double figure 8.
12. Place on parchment papered baking pans (or Silpat). Or, if you like, place each into a greased loaf pan for a taller loaf.
13. Chill remaining egg wash, covered, to use later.
14. Loosely cover breads with greased plastic wrap and let rise at warm room temperature for an hour or so.
15. Preheat oven to 350°F (175ºC).
16. Brush tops of babkas with remaining egg wash.
17. Bake about 40 minutes.
18. Transfer loaves to a rack and cool to room temperature.