Finely grate the peel of 2 limes and squeeze the juice out of all 4.
Peel and core the avocados and puree with the magic wand along with the lime juice, zest and powdered sugar. Whip the cream until stiff and add sugar to taste. Mix the avocado cream and cream together until smooth.
Chill in the refrigerator for about 1/2 hour. Garnish with lemon balm.