Prepare and store crumb topper in an airtight container at room temperature up to 24 hours. Prepare cherry filling, cool 30 minutes, then cover and chill overnight; reheat before serving. Chill meringue topper up to 4 hours before toasting or up to 2 hours after toasting.
Spread one 13-ounce container marshmallow creme to form a 1/2-inch-thick rectangle. Broil as in Step 4.
If you're making mini crisps, drop meringue by spoonfuls. If serving family-style, spread into a 1/2-inch-thick rectangle, swirl, and let guests scoop their own.