Preheat the oven to 150°C/300°F/Gas Mark 2. Put the egg whites into a bowl and whisk until stiff peaks form. Gradually whisk in the caster sugar, then fold in the almonds.
Grease two 20-cm/8-inch sandwich tins with butter and line with greaseproof paper. Divide the meringue mixture between the tins and level the surfaces. Transfer to the preheated oven and bake for 30 minutes. Remove from the oven. Leave to cool on a wire rack.
Put the cream into a bowl, add the icing sugar and whip until softly peaking.
Put one of the baked meringues onto a cake stand or serving plate and spread over a generous layer of the cream. Top with a generous layer of raspberries, then cover with the remaining meringue. Spread the remaining cream evenly over the top of the cake, and chill in the refrigerator for at least 2 hours.
Remove from the refrigerator, decorate with raspberries and fresh mint leaves and serve.