Place a 20-25cm/8-10in stainless steel ring onto the flan case and use it to cut through, discarding the outer sponge.
Cut the flan in half, to get two thin layers.
Place the steel ring onto a large flat plate and place one of the sponge layers inside and press down lightly.
Sprinkle two tablespoons of the Drambuie over the sponge then set aside.
Place the double cream into a bowl with the vanilla extract, the remaining Drambuie and 75g/3oz of the sugar and whip to soft peaks.
Line the flan ring with the largest strawberry halves, cut side against the ring. Reserve the rest of the strawberries.
Carefully place the whipped cream into the centre of the flan and spread out gently to fill the whole mould – adding as much cream as necessary to fill to the top of the strawberries.
Place the remaining flan case on top and press down lightly.
Remove the ring by carefully warming the edges with a hot cloth and lifting it straight off.
Dust the top with the icing sugar.
Place the remaining caster sugar into a very clean frying pan and place on the stove to caramelise.
Once it is caramelised remove from the heat to cool slightly.
While this is cooling, take a hot metal skewer that is red hot and score the topof the gateau in lines to create a diamond style pattern.
Dress the top of the gateau with the leftover strawberries and berries and garnish with sprigs of fresh mint.
To finish, dip a small spoon into the sugar and twist around a long narrow cylinder, like a steel used to sharpen knives, or even a wooden spoon handle, to create some curls then balance on top of the gateau.
Serve cut into wedges with more pouring cream if needed.