Make the frosted rose petals the day before. Separate the petals and spread the caster sugar over a plate. Holding one petal at a time, lightly paint both sides with egg white. Spoon sugar over it, then using tweezers, shake off the excess. Dry on baking parchment for a day.
Preheat the oven to 180C/gas 4/fan 160C. Butter two 20cm/8in round sandwich tins and line their bases with baking parchment. Tip the sugar into a mixing bowl and add the softened butter. Beat for a minute or so until pale and fluffy, then beat in the egg yolks.
Sift the flour and baking powder over the cake mixture. Fold in as lightly as you can using a large metal spoon, then fold in the almonds and extract. Stop folding as soon as the flour traces have gone.
Whisk the egg whites until they just hold their shape. Gently fold a third of the egg white into the cake mix, using the whisk. Repeat with another third, then the final third. Take care not to over-mix and lose the lightness of the egg whites.
Lightly fold in the raspberries. Divide between the prepared tins and level the mixture using a round-bladed knife. Bake for 30-35 minutes. Cool in the tin for 5 minutes, then turn out, peel off the lining paper and leave to cool completely.
Set one cake on a serving plate or cake stand. Spoon the cream on to the cake with a dessertspoon. Scatter the raspberries over and put the other cake on top. Blend the icing sugar with 1-11⁄2 tbsp cold water until it is smooth and coats the back of a spoon thinly. Drizzle the icing over the cake. Scatter the rose petals over and around the cake, dust with icing sugar and serve.