1. COMBINE flour, sugar, cocoa and butter in a food processor and process just until mixture resembles breadcrumbs. Add the egg and process briefly to combine. Turn onto a lightly floured surface and gently knead to form soft dough. Wrap and chill for at least 30 minutes.
2. ROLL out the pastry between 2 sheets of baking paper to line a 23cm round fluted tart pan with a removable base. Prick well with a fork and bake in a moderately hot oven 190°C for 10-15 minutes or until lightly browned. Scatter the base with the chocolate.
3. COMBINE the orange rind and juice with the caster sugar. Whisk to dissolve the sugar and then add the sour cream, eggs and flour and whisk until smooth. Pour the mixture into the pastry shell and smooth over the top. Scatter over the almonds.
4. BAKE in a moderately slow oven 160°C for 55-60 minutes or until set and golden. Cool in the pan before removing. Serve sliced with a dollop of cream and a sprinkle of extra almonds.