Remove frozen yogurt from freezer 10 min. before you plan to begin so it thaws slightly. Melt the butter.

Place the graham crackers in a large resealable plastic bag. Fold a dish towel around the bag and roll a rolling pin over the bag until you get coarse crumbs. Mix half the crumbs with the melted butter and set the other half aside.

Press the buttered cracker crumbs evenly on the base of a 9-inch springform pan (they won't form a cohesive crust, but that's OK). Spoon the first carton of frozen yogurt over the cracker crumbs and smooth the top with the back of the spoon.

Sprinkle remaining cracker crumbs and half of the raspberries over the frozen yogurt. Top with the second carton of frozen yogurt and smooth the top with the back of the spoon. Freeze for 5 hours or overnight.

Carefully unmold cake from the springform pan leaving the base for serving. Decorate with remaining raspberries, blueberries, and whipped topping.