Preheat the oven to 180C/ fan 160C/ Gas 4. Put the almonds on a baking tray and bake on the top shelf of the oven for 5 minutes. Remove and leave to cool.
Whisk the egg whites until they form stiff peaks. Whisk in the caster sugar, a little at a time, until the mix thickens.
Reserve 30 almonds for decorating, then blitz the rest in a food processor to a medium coarse powder. Fold the almonds and rice flour into the egg whites, then fold in the almond extract. Cover and chill for 30 minutes.
Spoon the mixture onto baking sheets lined with nonstick baking paper. Put an almond on each. Bake on the top shelf of the oven for 12 minutes. Cool on a wire rack.
Turn the cooled biscuits over and dip the base in melted dark chocolate and leave to set. Drizzle with melted white chocolate, then leave to set completely and pack into boxes or clear cellophane bags.
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