8 dark chocolate squares (about 1 1/2 ounces each)
8 graham crackers
1 firm but ripe banana
1 tablespoon melted butter
8 large marshmallows
Prepare a medium-hot fire in a charcoal or gas grill. Grease the grill grates with oil.
Break the graham crackers in half and arrange them on a large tray. Place a chocolate square over 8 of the halves, and set the tray near the fire or in direct sunlight to partially melt the chocolate.
With the banana still in its skin, cut it in half lengthwise. Brush the cut sides with the melted butter. Place the banana halves on the grill, cut sides down, and cook until deep grill marks appear but the banana is still relatively firm (not mushy), about 2 minutes. Remove the bananas from the grill and peel. Cut each half into 4 segments and place them, cut sides down, over the chocolate squares.
Meanwhile, put the marshmallows on skewers and toast over the grill until lightly charred and oozy, about 2 minutes. Place the marshmallows over the bananas and top with the other graham cracker halves to form sandwiches. Serve immediately.