For the shortcrust pastry, stir the butter, powdered sugar and salt until frothy. Stir in the flour and almonds with the water, gather the dough into a ball with your hands and wrap in foil. Chill for about 1 hour.
For the filling, heat the butter with the chocolate in a water bath while stirring until the chocolate has melted. Transfer to a mixing bowl, stir in the sugar, almonds, walnuts, cocoa and finally the milk. Put aside.
Roll out the shortcrust pastry into a rectangle about ½ cm thick between 2 layers of cling film. Halve the sheet of dough. Spread the chocolate filling on one half and place the other half on top.
Bake in the oven preheated to 160 ° C for 25-30 minutes, remove and allow to cool. Then very carefully cut into rectangles, diamonds or triangles with a sharp knife. Garnish with melted chocolate if you like.
Let it stand for at least a day in airtight seal so that the dough is nice and tender.