Put together this quick and easy dessert while your main dish cooks. Just before serving, toast the sweet sandwich until the chocolate filling is warm and gooey. It pairs beautifully with fresh fruit.
Heat a grill pan or a large heavy nonstick skillet over medium-low heat. Meanwhile, brush one side of each bread slice with some of the melted butter. Place half of the bread slices on a work surface, buttered side down; sprinkle with chocolate, covering the bread to within 1/4-inch of the crust. Top with remaining slices, buttered sides up. Place sandwiches, 2 at a time, in grill pan; weigh down top of sandwiches with a large heavy skillet.
Grill the sandwiches over medium-low heat for 6 to 8 minutes or until the chocolate is melted and bread is golden brown, turning once halfway through grilling time. Repeat with remaining sandwiches. (Or preheat a covered indoor grill. Place sandwiches, two at a time, in preheated grill, cover, and grill 4 minutes or until chocolate melts and bread is golden.)
To serve, cut each sandwich into quarters. Dust with powdered sugar. Serve warm.