Kristine Radzvilla Chocolate Swirl Babka

Ingredients

• 1/3 cup milk
• 1 package active dry yeast
• 1/2 cup sugar
• 2 sticks (1 cup) unsalted butter
• 4 large egg yolks (reserve 2 whites for meringue)
• 4 cups sifted all-purpose flour
• dash salt
• 2 oz. good-quality bittersweet chocolate
• 1/4 cup sugar
• 1/2 stick (1/4 cup) butter
• 1/4 cup milk
• 1 tsp. vanilla
• 2 egg whites