Puree 1/2 of the thawed berries with a Tbsp of the superfine sugar and a squeeze of lemon in a blender. Puree until smooth and adjust the consistency with a little water until the puree coats a spoon. Strain through a sieve (optional)Spoon a few teaspoons of the puree in the bottom of a champagne flute. Gently fill the glass with champagne. Garnish with a few berries.