Sponge Cake: Preheat the oven to 170 degrees C. Grease and line with baking paper two 23cm round layer cake tins.
Sift the flour, baking powder and salt together.
Separate the eggs and set the egg whites aside. Beat the egg yolks together on medium-high speed until very thick, about 4 minutes. Gradually add the cold water. Slowly add the white sugar and beat well for about 3 more minutes. Add 1 teaspoon vanilla. Sift the flour mixture over the egg yolk mixture and fold in.
Beat the egg whites and cream of tartar together until stiff peaks form. Fold this into the yolk mixture. Divide batter between the cake tins.
Bake for 25 minutes. Cool on rack for 10 minutes and then invert and cool completely.
Ricotta Cheese Filling: Beat the ricotta cheese well then add the icing sugar and cinnamon. Add the vanilla and grate the chocolate in using the coarse side of a grater. Stir in the candied lemon peel and mix. Chill until ready to use.
Rum Syrup: Place the sugar and the water in a small saucepan. Bring to a boil over medium heat stirring to dissolve sugar. Boil for 1 minute and then remove from heat and add the rum. Cool to room temperature.
Chocolate Glaze: Melt the chocolate and the cream in the microwave, whisk smooth. Add the butter and whisk until dissolved. Cool the mixture until spreadable.
To Assemle: Cut each cake layer in half. Place one of the 4 halves on a cake board or plate and sprinkle with a little of the rum syrup. Spread about 1 1/2 cups of the ricotta cheese filling over this layer. Add a second layer of cake and repeat this procedure. Top the cake with the last layer of cake. Chill at least 4 hours.
Before serving spread the chocolate glaze over top of cake.