Bring the milk to a boil with the lemon peel, the cinnamon stick and the sugar, stirring constantly, and then remove from the stove.
Remove the peel and cinnamon stick. Slowly pour in the semolina stirring constantly to avoid any lumps. Return the pot to the stove and simmer for another 5 minutes. Remove, stir in the butter and let cool.
Beat 1 whole egg with 4 egg yolks together and mix into the semolina. Set the the egg whites aside. Mix the ricotta cheese with the two liqueurs and some lemon zest. Add this to the semolina.
Whip the remaining egg whites until stiff and fold in to the semolina-ricotta mixture. Butter a shallow baking dish and dust with sugar. Pour in the mixture and place in an oven at 325°F. Bake for 45 minutes. Remove from the oven and let cool.
Cut the cake into squares and dust with frosting sugar, before serving.
Serves 4
