1) Rub raspberries through a sieve into a bowl and make a thick puree.
2) Add sugar to sweeten.
3) Add yogurt and lemon juice into it.
4) In a small bowl stir 4 tablespoons of cold water and sprinkle gelatin on it.
5) Let stand for 5 minutes.
6) Place the bowl over a pan of hot water.
7) Stir till the gelatin dissolves and liquid is clear.
8) Blend liquid gelatin and raspberry puree.
9) In another bowl, beat egg whites until stiff. Fold into puree.
10) Transfer content into a container, cover with a lid, and set in the freezer.
11) When frozen, beat with rotary beater.
12) Freeze firmly.