Chocolate-Raspberry Panini with Mascarpone

Name: Chocolate-Raspberry Panini with Mascarpone
Yield: makes 4 Servings
Ingredients: 1/4 cup (1/2 stick) unsalted butter, room temperature; 8 4x3x1/2-inch slices French bread; 4 tablespoons raspberry preserves; 32 fresh raspberries; 4 ounces bittersweet chocolate (do not exceed 61% cacao), coarsely chopped; 6 tablespoons mascarpone cheese; 8 teaspoons (packed) golden brown sugar