My husband requested a birthday cake with marzipan flavoured fluffy frosting. This is what I came up with. This is derived partially from the recipe for uncooked buttercream in Stephen Schmidt's "Master Recipes"
12 tablespoons of butter
4 tablespoons of almond paste
--- this is a rough estimate on the almond paste amount - I laid the tube of Odense Pure Almond Paste next to the 4 tbs of butter, and cut off that amount. I am following Sherry Yard's suggestion that almond paste can be substituted 1 for 1 for the fat in many recipes.
2 large egg yolks
1/4 tsp of salt.
1 lb confectioner's sugar
2-3 tbs amaretto liqueur
1-2 tsp of cold milk.
Cream butter, egg yolks, salt and almond paste until the mixture turns very pale - almost white, and the almond paste is fully incorporated.
Add the confectioner's sugar a cup at a time, alternately with tablespoon fulls of amaretto, beating well after each addition. I finished off by blending in a little bit of milk, since I thought the frosting was a little stiff, and that the flavour was very pronounced. The tiny bit of milk softened and mellowed it nicely, and made a bit fluffier.
Results: this came out pretty well, though whether it fit's hubby's vision of a fluffy marzipan frosting remains to be seen. The almond paste keeps it from being perfectly smooth and creamy -- there is a granular look too it, though it is not too noticeable in the mouth. The almond/marzipan flavour is very clear, though I think it may be a little too sweet -- the almond paste contains sugar of it's own, whereas the butter wouldn't have.
On the other hand - I think all whipped frostings are excessively sweet, so that could just be my palate. This frosting is going to go on a coffee flavoured cake, filled with a light ganache of about 50/50 bittersweet/semi-sweet chocolate, so I think that the sweetness of it will be moderated by the final cake.
I'm betting that I could push the almond paste percentage to 50% of the total fat in this, if I were willing to accept a less fluffy and more sweet frosting.... As it is I have a nice fluffy frosting with a nice clear pure marzipan flavour.