Heat the oven to 180C/160C fan/gas 4. To make the gooseberry purée, tip 200ml water and the sugar into a pan and heat, stirring, until the sugar has dissolved. Bring to a gentle simmer, then add the gooseberries and cook for 8 mins, or until tender. Drain, reserving the poaching liquid. Lightly mash the gooseberries to break them up a little, then leave to cool. Taste to check for sweetness, and add a little more sugar if you like (remember that the cream and sponge are both sweet, though). Boil the reserved poaching liquid for 8-10 mins until syrupy, then add the cordial. Leave to cool completely.
Butter and line the base of a 20-23cm cake tin. To make the sponge, beat the eggs and the sugar together with an electric whisk until pale and tripled in volume, then add 1 tbsp lukewarm water. Fold in the flour and a pinch of salt using a large metal spoon, being careful not to knock the air out of the eggs. Pour into the prepared tin and bake for about 25 mins. When ready, it will come away slightly from the edges of the tin. Leave to cool in the tin, then turn out and cut into broad fingers. You should get about 18, but don’t worry about accuracy – there’s no need to be precise.
For the cream, beat the mascarpone with a wooden spoon to loosen it, then add the crème fraîche and sugar. Gradually add the cordial and squeeze over some lime juice. Taste and check whether you need more sugar, cordial or lime juice, then transfer to the fridge and chill until needed.
Arrange a layer of sponge fingers over the base of a glass bowl or trifle dish, then spoon over some of the elderflower-flavoured poaching liquid. Top with a layer of gooseberry purée, then a layer of the cream. Continue to layer the ingredients (you’ll probably only manage two layers of each), finishing with a layer of cream. Chill for at least 2 hrs and up to two days, then garnish with some toasted flaked almonds and flowers before serving.