Preheat the oven to 170 C / Gas 3. Grease and line with baking parchment two 23cm round cake tins
Sieve 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. Add 250g caster sugar, slowly and beat well for about 3 more minutes. Add 1 teaspoon of the vanilla. Sieve 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 tins.
Bake at 170 C / Gas 3 for 25 minutes. Cool on rack for 10 minutes and then invert and cool completely.
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 (see below). Spread about 1/3 of the filling over this layer. Add a second and third layer of cake and repeat this procedure. Top the cake with the last layer of cake. Chill at least 4 hours. Spread chocolate glaze (see below) over top of cake.
To Make Ricotta Cheese Filling: Beat the ricotta cheese well and add the icing sugar and cinnamon. Add 1 1/2 teaspoons of the vanilla and grate 60g of the chocolate in using the coarse side of a grater. Stir in the mixed peel. Chill until ready to use.
To Make The Rum Syrup: Place 65g sugar and the water in a small saucepan. Bring to the boil over medium heat, stirring to dissolve sugar. Boil 1 minute and then remove from heat and add the rum. Cool to room temperature.
To Make The Chocolate Glaze: Melt 175g chocolate and the cream in the microwave, whisk smooth. Add the butter and whisk until dissolved. Cool mixture until spreadable. Spread over the top of the cake.
Cake flour can be made by mixing together 185g plain flour with 30g cornflour.