Chocolate Frosting with Custard Base

I've been interested in making this version of chocolate frosting for a while. It is custard based frosting. It turns out light tasting, very good. Although with most buttercream frostings there is a gross amount of butter! Oh well... it's Valentines!

2/3 cup whole milk
3 large egg yolks
1 tbsp plus 1tsp flour
1 + 1/3 cup icing sugar
1 tsp vanilla
3 sticks (1 1/2 cups) unsalted butter softened cut into tablespoon pieces
8 oz milk chocolate melted and cooled
2 oz unsweetened chocolate melted and cooled

I only had semi sweet so I used all semi sweet instead.

Heat milk in heavy saucepan over moderate heat until hot. In another heatproof bowl whisk together yolks, flour, only 1/3 cup of the icing sugar, and a pinch of salt. Add the milk to this mixture in a steady stream whisking. Transfer the mixture back to the saucepan and bring to a boil over moderate heat, whisking. Reduce heat and simmer, whisking approx two minutes. You have to be very careful at this stage, you could go too far and end up with lumps, just pull pan off the stove if it is getting too hot, and stir, then put back on, with lowered heat. Once thickened transfer to a bowl and cover the surface of the custard with a buttered round of wax paper and cool approx 45 minutes.

Add vanilla and remaining cup of icing sugar to custard in mixer. Beat with beaters at moderate spread and then increase speed to medium high and beat in butter 2 tbsp at a time until smooth. Add the cooled chocolate and beat until combined.

The flower was made with marshmallow fondant. Basically you melt marshmallows in microwave with a tiny bit of water and knead in icing sugar to a 'playdoh' like consistency.