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. Grate over orange zest if you are using it, then mix with the ground almonds in a large bowl.
Melt chocolate and butter over hot water
Separate the eggs, setting the whites aside. In large bowl beat the egg yolks well with half the sugar
Stir in the chocolate mixture and the almonds. It will get quite stiff
Whisk the egg whites with pinch salt until they form stiff peaks and then gently fold into the mixture. Pour the mixture into the prepared tin. Bake for 30 – 35min until set on the sides a slightly moist in centre.
Allow to cool in the tin for a while before turning out.