This is a really pretty celebratory cake. Soft, buttery yellow cake layers, filled and frosted with a gorgeous white chocolate orange Ganache buttercream. If you like, you can increase the amount of the orange flower water, and the filling will almost resemble a bitter orange marmalade in taste. Speaking of the Ganache buttercream, depending on how you plan to decorate your cake, use a third of it for the filling, or even more, if you just plan to simply spread it all over the cake.
If you are making the cake for a special occasion, you can dye the frosting to your liking, but I recommend using gel food colouring, for two reasons. One, you use significantly less colouring, thus not risking it will change the flavour of the frosting. And two, the colours are more vibrant. On the side note, if your frosting is too thick to be piped out of small nozzles (like the Wilton grass tip, 233), thin it with additional milk or cream. For the grass tip, I needed to add about 3-4 more tablespoons of cream, to make it pipeable.
For the cake
150 grams plain flour
50 grams cornflour (corn starch)
2 teaspoons baking powder
120 grams softened butter
200 grams sugar
1 teaspoon vanilla
120 ml whole milk
2 large eggs, separated
100 grams real white chocolate, roughly grated
For the filling
250 grams softened butter
200 grams icing sugar
50 grams instant vanilla pudding powder
100 ml whole milk
200 grams real white chocolate
120 ml heavy whipping cream
1 teaspoon orange flower water
Separate the eggs into yolks and whites, place them into separate bowls and let them sit at room temperature for about 30 minutes. Sift together the plain flour, cornflour (corn starch) and baking powder and set it aside. Take a large bowl, add the butter and beat with an electric mixer on high for about 2 minutes, until light and fluffy. Add half of the sugar and continue beating for about 3 minutes more. Scrape the sides of the bowl, if needed. Add the vanilla and one egg yolk and beat it in well. Add the other yolk and blend completely. Turn the mixer down to low and add in the flour mix and the milk in a few additions. Mix until just blended.
In another bowl (glass or metal, preferably) beat the egg whites until soft peaks form. Gradually add the rest of the sugar, beating on high constantly, until stiff peaks form. Add the roughly grated white chocolate to the batter, then gently fold in the whites, being very careful not to overmix and deflate the batter. Generously grease and flour a baking pan (15x30 cm; 6x12"), pour in the batter and level it as much as possible. Bake it immediately, in a preheated oven, at 180˚C (350˚F), for about 25-30 minutes. Check it with a toothpick to make sure it does not overbake. Let the cake cool in the pan for about 10 minutes, then take it out and place it on a wire rack to cool completely.
For the filling, chop up the chocolate, put it in a heavy bottomed pan and pour over the heavy whipping cream. Melt it slowly over medium high heat, until it becomes smooth and shiny. Remove from heat and let it cool down to room temperature, then place it in the fridge for about an hour. When the cream filling has cooled down, take a large bowl and beat the softened butter with an electric mixer on high, for about 3 minutes, until lighter in colour.
Add the instant vanilla pudding powder and blend it into the butter. Sift in half of the icing sugar and blend it well. Add half of the milk and the other half of the icing sugar and blend again. Finally, add the orange flower water and the rest of the milk and beat until combined. When it becomes fluffy, add the white chocolate Ganache, spoonful at a time, beating on low constantly. The filling should be smooth and creamy.
Once the filling is ready and the cake is cooled, level the cake if necessary, then cut it in half lengthwise. Place half of the cake on the platter, gently and evenly spread about a third or so of the filling, and level it as much as possible. Place the other cake layer on top of the filling and press it gently with the palm of your hand. Take more frosting and frost the entire cake in an even layer, then place it in the fridge for 30 minutes. Take the chilled cake out of the fridge, and decorate it to your liking using the rest of the Ganache buttercream. Place the cake in the fridge for at least 8 hours or overnight.Note: If you are not serving the cake on the day it's made, brush the layers with simple syrup, to make sure it stays moist and fresh.