In a medium saucepan, warm the milk over low heat until it is just lukewarm, about 110 F. Place the milk into a medium bowl and add yeast – whisk the two together. Stir in the flour; cover with plastic wrap and let rise until doubled, about 30 minutes.

In a large mixing bowl, beat together the butter, sugar and salt until soft, about 2 to 3 minutes. Beat in vanilla paste and extract. Add 6 egg yolks, one at a time, beating until smooth after each one.

Mix in about 1/3 of the flour, then 2 more egg yolks. Scrape down the bowl and beater. Add another 1/3 of the flour and 2 more yolks and scrape down again. Mix in the remaining flour and egg yolks.

Add the sponge mixture into the mixing bowl. Mix on low for 2 minutes. Let the dough rest for 10 minutes.

Beat the dough on medium until it is smooth and elastic, about 2 minutes; the dough should be very soft. Add chocolate chunks and mix until combined.

Scoop the dough into a buttered 12 cup bundt pan. Cover and let the dough rise until it doubles, about 60 minutes.

Preheat the oven to 350 degrees, with the rack in the center of the oven, 15 minutes before the dough has completely risen.

Bake until well risen and very golden, about 40 to 45 minutes. I used a cake tester in the center of the bread to be certain it was done.

Remove and cool in the pan on a rack for about 10 minutes. Then invert the babka onto a rack and cool completely.