In a small saucepan, heat the cream until steaming. Remove from the heat, add the chocolate and stir until melted. Transfer the mixture to a shallow bowl and refrigerate until firm, about 2 hours.
In a standing electric mixer fitted with a paddle, combine the warm water with the yeast and let stand until frothy, about 5 minutes. Add the flour, milk, granulated sugar and salt and mix at low speed until the dough just comes together, about 1 minute. Add 2 tablespoons of the butter and mix, scraping down the sides occasionally, until a smooth dough forms, about 5 minutes.
Turn the dough out onto a lightly floured surface and knead until smooth. Transfer the dough to a lightly oiled bowl, cover and let rise in a warm place until doubled in bulk, 1 to 1 1/2 hours.
On each of 2 heavy baking sheets spread the remaining 8 teaspoons butter into four 5-inch rounds; use the full teaspoon for each round. Neatly sprinkle 1 tablespoon of the confectioners' sugar over each buttered round.
Punch down the dough and divide it into 8 pieces; work with 1 piece at a time and keep the rest covered with plastic wrap. Divide the first piece of dough in half. On a lightly floured surface, press each half into a 3-inch round, slightly thicker in the center and thinner around the edges. Lightly brush the edges with water and spoon 1 tablespoon of the cold chocolate filling into the center of one piece. Top with the other piece and press the edges together to seal. Pinch and smooth the seam as you form the dough into a smooth ball. Set the ball on one of the sugared rounds on the baking sheet. Repeat with the remaining dough and filling. Loosely cover the bomboloncini with plastic wrap and let rise in a warm, draft-free place for 45 minutes.
Preheat the oven to 400°. Bake the bomboloncini in the middle of the oven, 1 sheet at a time, for about 10 minutes, or until puffed and golden and the confectioners' sugar on the baking sheet is lightly caramelized. Using metal tongs, carefully swirl the bomboloncini in the caramel and invert them onto a wire rack to cool for 5 minutes. Transfer the bomboloncini to plates and serve warm.