Heat the oven to 180C/400F/gas mark 6. Generously butter and flour a 26cm cake tin, with a loose bottom if you like.
If you are using a food processor and whole almonds, pulse the nuts a few times, then add the roughly chopped chocolate and pulse until you have a coarse mixture.
If you are doing everything by hand, chop the chocolate finely with a sharp knife, grate over orange zest if you are using it, then mix with the ground almonds in a large bowl.
Add the sugar, salt and milk to the almond and chocolate and mix. Separate the eggs, setting the whites aside. Then beat the egg yolks into the mix one by one.
Whisk the egg whites until they form stiff peaks and then fold into the mixture, then scrape the mixture into the prepared tin.
Bake for 40-50 minutes or until the cake is firm and just turning golden, and a skewer or piece of spaghetti inserted comes out clean.
Allow to cool in the tin for a while before turning out.