Chocolate Bread Pudding

Name: Chocolate Bread Pudding
Ingredients: 5 ounces unsliced challah, or unsliced or sliced brioche bread; 1 tablespoon unsalted butter, plus more for the baking dish; 4 ounces semi-sweet chocolate or heaping 1/2 cup semi-sweet chocolate chips, divided; 1/4 cup granulated sugar; 1 tablespoon natural unsweetened cocoa powder; 1/4 teaspoon instant espresso powder (optional); 1/4 teaspoon kosher salt; 2 large eggs; 1 cup whole milk; 1 teaspoon vanilla extract; Powdered sugar and/or vanilla ice cream, for serving (optional)