1 Juice 3 oranges. Peel one orange with a sharp knife, removing all the white pith and membrane. Then slice the orange. Strain the blood orange juice through a sieve, then put into a pan with 60 g sugar and heat.
2 Soak the gelatine in plenty of cold water. Then squeeze out and dissolve in the hot juice. Stir in the prosecco.
3 Pour into 4 glasses and leave to cool. As soon as the liquid begins to set, place a slice of orange on top of each and put into the refrigerator for about 3 hours to set.
4 Whip the cream with 1 tsp sugar until stiff. Put a small spoonful on top of each portion of jelly and serve garnished with lemon balm.