Place a large piece of plastic wrap on a flat surface. Slice the cake into 1-inch-thick pieces and lay it on the plastic wrap to form about a 10- X 16-inch rectangle. Cover with a second piece of plastic wrap and roll with a rolling pin to press cake pieces together.

Place yogurt in microwave and defrost for about 1 minute to soften. If you do not have a microwave, soften yogurt in the refrigerator for 20 to 30 minutes. Spread yogurt evenly across cake and roll up lengthwise; wrap tightly in plastic wrap and freeze until firm, about 2 hours.

To serve, cut into 1-inch-thick slices and drizzle each slice with 1 tablespoon of fudge sauce. Yields 1 slice per serving.