For Mousse :
Blanch pistachio in boiling hot water. Grind with little water to make puree. combine pistachio puree with sugar in a medium bowl.
Soften gelatin in lemon juice, stir into dissolve over hot water. Stir into puree.
Beat egg whites until foamy and add to puree. Place mixture in freezer. When partially frozen, for about 45-60 minutes, beat in a food processor or blender until pale in color.
Transfer to bowl. Whip one cup of cream and fold into mixture. Add the chopped pistachios.
For Assembly :
Slice the vanilla sponge cake in to two layers.
Soak the lower layer with sugar syrup. Place gulab jamun cut into half to cover the whole layer.
Cover with pistachio mousse and level before placing the second layer repeat the process and finish off with a sprinkle of chopped pistachios and decorate however you wish. The yummy Gulab Jamun ‘n’ Pistachio mousse cake is ready