Preheat oven to 180°C. Line a 7 inch round cake pan with grease proof paper.
Place Dr. Oetker Nona Sponge Cake Vanilla, eggs and water in a mixing bowl. Mix at high speed for 6 minutes. Add in butter and mix at low speed for 1 minute or until batter is light and fluffy.
Pour the mixture into the cake pan. Bake at 180°C for 30 minutes.
Turn the cake out onto a wire rack, set aside until the cake completely cool.
Beat the whipping cream at medium speed until stiff peaks form.
Slice the cake into half (horizontally) using a long serrated knife.
Place half of the cake on a serving plate. Spread a layer of whipped cream and top with chocolate chips. Lay another half of cake on top and cover the top and sides of the cake with whipped cream.
Trace a 7 inch circle on a baking paper with your desire number in the centre. Cut out the number and place it on top of the cake. Sprinkle blue crystal sugar over the top of the cake. Gently lift off the number and place the traced baking paper on top of the cake, sprinkle with yellow crystal sugar.