In a microwave safe bowl, combine semisweet chocolate chips, heavy cream, and, if desired, coffee liqueur. Heat the mixture in microwave on high (100% power) for 1 to 1 1/2 minutes, then whisk until smooth.
Brush pound cake slices with melted butter. For a charcoal or gas grill, grill cake slices on the greased rack of an uncovered grill directly over medium heat for 1 to 2 minutes or until toasted and heated through, turning once halfway through grilling.
Skewer 3 marshmallows on each of four 12-inch wooden skewers. For a charcoal or gas grill, toast marshmallows just above rack directly over medium heat 3 to 4 minutes, turning as needed to soften marshmallows and brown all sides (toast one skewer in each hand at a time or enlist help).
Serve grilled cake slices with chocolate sauce, crumbled graham crackers, and marshmallows on top.
From the Test Kitchen
Caramel Sauce Option
In a small saucepan, cook and stir unwrapped vanilla caramels and whipping cream over low heat until smooth.
Serve on top of cake with marshmallows and crumbled graham crackers instead of chocolate sauce.