Photograph: Jan Baldwin
Line a 7cm-deep 22 x 10cm loaf tin with clingfilm so it overhangs the edges all the way round. Whiz the 300g of raspberries in a food processor with half of the icing sugar. Sieve the purée into a bowl, discarding the pips.
Whip the cream with the rest of the icing sugar to soft peaks. Fold the custard into the cream and divide between two bowls. Stir the raspberry purée into one bowl.
In another clean bowl, whisk the egg whites to soft peaks. Fold half of the egg whites into each custard mixture. Spoon the two mixtures into the prepared loaf tin, alternating spoonfuls of each mixture. Reserve a couple of tablespoons of mixture to use on top of the sponge fingers. Use a skewer to gently swirl the mixtures together.
Pour the sherry into a shallow bowl. Dip both sides of the sponge fingers into the sherry and place on top of the mixture in two layers. Finish with a thin layer of the leftover mixture. Cover with the clingfilm and freeze overnight.
For the praline, gently melt the sugar in a small pan. When it has turned to a golden caramel, stir in the flaked almonds and tip on to a sheet of nonstick baking paper. Leave to set.
Transfer the terrine from the freezer to the fridge 30 minutes before serving. Tip it out of the tin, remove the clingfilm and scatter with the praline, broken up, and the extra raspberries. Slice to serve.
Note: this recipe contains raw / partially cooked eggs.
Get ahead: make up to 2 weeks ahead.