Melt the butter in a small pan over low heat with the white chocolate. Stir and leave to cool a little.
Whisk the egg white in a large bowl until frothy, but not stiff.
Sieve in the icing sugar and whisk.
Gently stir in the melted butter mixture followed by the rhubarb.
Sieve in the buckwheat flour and fold in together with the ground almonds.
Divide the mixture between 12 silicone mini cupcake cases.
Bake for about 15 minutes at 180℃ (350℉, Gas 4) until golden, firm and well risen.
Leave to cool for a little, then turn out onto a wire rack to cool completely.
The recipe can easily be doubled, tripled or quadrupled for more of these delicious morsels.Please note: calories and other nutritional information are per serving. They’re approximate and will depend on exact ingredients used.