Bake or purchase angel food cake. When cooled, tear cake into pieces. In a 2 quart glass bowl, add 1/3 of the cake pieces to the bottom of the bowl. In a separate glass dish add raspberry gelatin (sugar free or regular). Pour 2 cups of boiling water on top. Add 1 bag of defrosted frozen raspberries. Mix and put in refrigerator for 15-20 minutes to thicken, not set. Add layer of raspberry –gelatin mixture to cake pieces and top with sugar free or low-fat raspberry yogurt. Repeat 3 times. Let set in refrigerator at least 2 hours