Individual Chocolate and Peanut Butter Bundt Cakes

Name: Individual Chocolate and Peanut Butter Bundt Cakes
Ingredients: 3/4 cup cream cheese (6 oz), softened; 1 1/4 cups chunky peanut butter (12 oz); 6 large egg yolks; 2/3 cup granulated sugar; 1/4 cup all-purpose flour; 1 1/4 cups unsweetened cocoa powder (not Dutch-process); 1 1/4 cups boiling water; 3 1/2 oz fine-quality bittersweet chocolate (not unsweetened), finely chopped; 1 (8-oz) container sour cream; 1 tablespoon vanilla; 2 cups all-purpose flour; 1 3/4 teaspoons baking soda; 3/4 teaspoon salt; 2 1/2 sticks (1 1/4 cups) unsalted butter, softened; 2 cups packed light brown sugar; 3 large eggs; Accompaniment: vanilla ice cream or whipped cream; 2 large pastry bags with 3/4-inch openings (or large heavy-duty sealable plastic bags with 1 corner snipped off) and 3 mini angel-food-cake pans (each with molds for six 6- by 3 1/2- by 1 3/4-inch cakes) or large-muffin pans (1 cup)