Chocolate-Filled Sweet Buns

1 package active dry yeast
1/2 cup warm water (105°-115° F.)
1/3 cup granulated sugar
1/3 cup plus 1 tablespoon milk
1/4 cup (1/2 stick) butter, melted and cooled
1 large egg
1/2 teaspoon salt
3 1/2-4 cups all-purpose flour

Filling
1/4 cup heavy cream
4 ounces (4 squares) semisweet chocolate, coarsely chopped

Glaze
2 tablespoons milk

In a large bowl, dissolve yeast in warm water. Let stand until foamy, 5 to 10 minutes.

Stir sugar, 1/3 cup milk, melted butter, egg, and salt into yeast mixture. Using a heavy-duty electric mixer fitted with the paddle attachment and set on low speed, beat in flour, 1/2 cup at a time, until a soft dough forms.

On a floured surface, knead dough until smooth and elastic, 5 to 10 minutes, adding more flour to prevent sticking. Place dough in a large greased bowl, turning to coat. Cover loosely with a damp cloth; let rise in a warm place until doubled, 1 hour.

To prepare filling, in a small saucepan, heat cream over medium heat until bubbles appear around edges of pan. Remove from heat. Add chocolate; stir until smooth. Press plastic wrap directly onto surface; freeze for 1 hour.

Grease a baking sheet. Punch down dough. Roll dough into a rope; cut into 10 equal pieces. On a floured surface, using a floured rolling pin, roll each dough piece into a 7 x 3 1/2-inch rectangle.

Spoon filling evenly into center of each rectangle. Brush edges with remaining milk. Fold dough over filling; press seams to seal; fold ends under. Place buns, seam-sides down, on prepared baking sheet. Cover again; let rise in a warm place until almost doubled, 1 hour.

Preheat oven to 400° F. Brush buns with milk.

Bake buns until golden and bottoms sound hollow when tapped, 25 minutes. Transfer to a wire rack to cool slightly.