Elderflower mousse
Bring the elderflowers and milk slowly to the boil, then turn off the heat. Cover and leave to infuse for 10 minutes. In a large bowl, whisk the egg yolks with 3oz/85g of the caster sugar until thick, pale and creamy.
Boil the milk again and strain. Pour it slowly on to the egg yolks, whisking constantly. Place the bowl over a pan of simmering water and stir until the custard is thick enough to coat the back of a spoon.
Put 4 tbsp of hot water into a small pan, sprinkle over the gelatine and leave for five minutes to swell. Then heat very gently until dissolved. Pour the gelatine into the hot custard and stir. Leave in the fridge to cool and thicken to the consistency of whipped cream.
Whisk the egg whites into soft peaks, sprinkle in the rest of the caster sugar and whisk again until stiff. Fold into the custard. Allow to set, then whip the cream and fold it in. Spoon into a 2.5 pint/1.25 litre mould or serving bowl, cover and leave to set in the fridge.