Crush the almonds as fine as possible in a mortar with one of the egg whites.Pass the ricotta through a strainer if it is hard or lumpy, then mix thoroughly with the almonds. Beat the rest of the eggs separately and then fold into the mixture along with the sugar and the lemon zest.
Now pour the mixture into a pudding mould greased with butter and dusted with breadcrumbs.
Heat oven to 170°C and bake for one hour until golden and quite dry inside: test the doneness with a skewer. Unmould and serve cold.