Step by step recipe:

1. 5 min.
   Tip 100 g ground almonds, 250 g flour, 125 g icing sugar, 1 egg into the bowl of your mixer and add 125 g butter cut into pieces.
2. 4 min.
   Knead on low speed for 3 or 4 minutes until evenly mixed.
3. 10 min.
   Crush 50 g chocolate into small pieces and add to the mixture with 1 teaspoon powdered cocoa. Knead for a further 2 or 3 minutes.
4. 1 hour
   Gather the dough together and form into a roll about 4 cm (2") diameter, then wrap in plastic film and refrigerate at least one hour or overnight.
5. 7 min.
   Preheat oven to 180°C (360°F).
   
   Remove dough from fridge and cut slices 0.5 cm ( ¼") thick.
   
   You will find that as you slice, the roll of dough will deform, so turn it as you go, and if necessary reshape the slices.
6. 3 min.
   Place the slices of dough on a baking sheet.
7. 20 min.
   Cook for about 20 minutes, then leave to cool on a wire rack.