Mix the Martini and gin together and
chill or store in a bottle if making ahead.
If you have room in your fridge or freezer,
chill your Champagne glasses, too.
When your guests are due to
arrive, spoon ½ tsp icing sugar into
8 Champagne glasses. Pour over the
Martini mixture, mix with a spoon and
add the frozen raspberries. Top up with
the sparkling wine just before serving.