Cut through the flan case using a 20-25cm stainless steel ring and discard the outer sponge.
Slice the sponge horizontally to create two thin layers.
Place the ring on a flat plate and press one sponge layer into the bottom.
Drizzle two tablespoons of liqueur over the sponge layer.
Whip the cream, vanilla, remaining liqueur, and 75g of sugar into soft peaks.
Line the inside of the ring with the cut sides of the large strawberry halves.
Fill the center with whipped cream, leveling it to the top of the strawberries.
Place the second sponge layer on top and press down gently.
Warm the ring edges with a hot cloth and lift it off carefully.
Dust the top of the gateau with icing sugar.
Melt the remaining caster sugar in a pan until it caramelises.
Remove the caramel from heat and allow it to cool slightly.
Score a diamond pattern on the top using a hot metal skewer.
Decorate the top with remaining strawberries, berries, and mint sprigs.
Spin the caramel around a handle to create curls and place them on top.
Serve in wedges with additional pouring cream if desired.