Make the pomegranate juice: wear an apron, it can get a little messy! Cut the pomegranates into sections and fill half a bowl with water. Separate arils and pulp under water. The bitter white pulp will float to the surface and the arils will sink to the bottom. Remove the pulp and strain the seeds from the water. You can now grind the seeds in a blender and then press the pulp with the round side of a spoon through a sieve over a bowl. If you don’t own a blender, you can also push the seeds through the sieve by hand, it will only require a little more effort.
Top up the juice with water to 500 ml (16 fl oz/2 cups) and place on the heat with the sugar and ginger slices. Reduce the syrup by half. Leave to fully cool and remove the ginger.
Pour a coffee spoon (to taste) of pomegranate syrup into an attractive glass. Add prosecco to fill the glass. Garnish the glass with a few loose pomegranate seeds.