Line a 900g (2lb) loaf tin with cling film, leaving an overhang and sprinkle the toasted almonds onto the base.
Soak the gelatine in a little cold water. Meanwhile, blitz 200g of the raspberries in a food processor with the icing sugar and two tablespoons of water. Sieve into a small pan and heat gently to warm through. Once the raspberries start to boil, remove from the heat.
Squeeze out the gelatine and add to the raspberry purée, stirring continuously until the gelatine melts. Crush the remaining 200g of raspberries with a fork, then combine with the raspberry mixture and allow to cool to room temperature.
Remove the ice cream from the freezer and allow to soften for 5 minutes. Spoon the ice cream into the loaf tin and smooth using the back of a spoon. Spoon the prepared raspberry mixture evenly on top of the ice cream and press the sponge fingers lightly onto the ice cream layer. Using the overhang of cling film, fold over the trifle and freeze until solid. Overnight is ideal.
Remove the trifle from the freezer about 15 minutes before serving. Tip the loaf tin upside down on a serving plate, then peel off the cling film and cut into slices. The trifle fingers will therefore be on the bottom of the trifle for serving.