Frozen Lemonade Squares

18 squares Honey grahams, finely crushed (about 1 1/4 cups crumbs)
1/3 cup margarine or butter, melted
1 quart (4 cups) frozen vanilla yogurt, softened
1 can (6 ounce) frozen lemonade concentrate, thawed
½ cup thawed Cool Whip whipped topping

Mix graham crackers and margarine. Press firmly onto bottom of 9-inch square pan.

Beat yogurt and lemonade concentrate in large bowl with electric mixer on medium speed until well blended. Spread over graham cracker crust. Freeze 4 hours or until firm. Cut into squares. Top each square with a dollop of whipped topping. Garnish with fresh lemon slices fresh raspberries, if desired. Store left overs in freezer.