Sprinkle gelatin over cold water to soften. Put yolks in top of a double boiler. Mix yolks with lemon juice, rind, and 3/4 cup sugar. Place over boiling water and cook, stirring constantly, until lemon mixture is slightly thick, about 8 minutes. Remove from heat and stir in gelatin until dissolved. Chill until mixture molds slightly when small amount is dropped from a spoon. Beat egg whites until they start to hold shape. Then add remaining 3/4 cup of sugar, about 1 tbsp. At a time, until sugar is used and egg whites are stiff. Transfer chilled lemon mixture to a large bowl. Add egg whites and cream and gently fold into lemon until no white streaks remain. Pour int a 2-quart souffle dish and chill at least 4 hours or until firm.
