Process nuts in a food processor until they have the texture of breadcrumbs. Melt butter with agave syrup and pour into nut mix. Add egg white and mix well with a spoon.
Line the base of 6 greased 6-cm (2-inch) rings with greaseproof paper. Spoon in and bake the nutbase in oven for 15 minutes. Remove and allow to cool in the tins (see next page).
Beat ricotta in a bowl with electric beaters until smooth. Stir in yoghurt, agave syrup, lemon, cornflour and eggs. Beat until completely mixed.
Fold through chocolate buttons and pour into prepared tins. Bake for 20 minutes in a moderate oven at 180°C (350°F/gas mark 4).
Remove from the oven and allow to cool. Remove from the tins and place onto serving platter.
Dust with a little icing sugar. Serve sliced with fresh berries.