Heat half the lemonade in a saucepan until almost boiling and remove from the heat. Squeeze out the gelatine and stir into the hot lemonade. Keep stirring until dissolved.
Pour in the remaining lemonade, the ginger ale, 250ml of the Pimms and the lemon juice. Strain through a sieve and leave to cool.
In a bowl, drizzle the strawberries with 20ml of the elderflower cordial, 50ml of Pimms and half of the icing sugar.
Lay a slice of Madeira cake at the bottom of 6 glasses. Distribute half the strawberries evenly on top and pour over the cooled Pimms mixture. Chill in the fridge for about 3 hours, or until the jelly has set.
Once the jelly is set, make the cream by whisking together the yogurt, mascarpone, 60ml of elderflower cordial and the other half of the icing sugar, until thick.
Spoon the remaining strawberries over the jelly, top with the elderflower cream and serve chilled. Garnish with a whole strawberry if desired.