Chocolatre frosting with sour cream

The #1 reason that puts me off making any kind of cake frosting is the amount of sugar and butter used in a recipe. I know without these two ingredients I won't achieve any good and stable frosting. So, I'm constantly googling for frosting recipes that are not so caloric. My search brought me to this recipe over at Kwanster.
I'm re-posting the whole recipe below in order for me to note down any tweaking needed to suit my taste. In saying that, it is already great recipe and you shouldn't hesitate to try it! And go over to Kwanster's blog to thank him/her.
Chocolate Sour Cream Frosting (for 12-15 cupcakes) via : link above
Ingredients
170g bittersweet chocolate, finely chopped ** used 60% cocoa content, find the taste to dominating..
64g unsalted butter, at room temperature
1 1/2 cups confectioners’ sugar, sifted ** didn't follow exactly, adjusting to taste as I whisk
3 tbsp. unsweetened cocoa powder, sifted
Pinch of salt, sifted
1/2 cup plus 1 tbsp. sour cream , room temperature **20% fat ** added rum for extra flavour
Method:

1. Melt the chocolate in a heat-proof bowl set over a pot of simmering water. Set aside to cool until just barely warm.
2. In the bowl of a stand mixer fitted with the paddle attachment, beat butter on medium-high speed until pale.
3. Gradually mix in the sifted confectioners’ sugar, cocoa powder and salt, beat until light and fluffy.
4. Beat in the melted and cooled chocolate and then the sour cream.
5. Continue beating until the mixture is smooth and well blended.
6. Frost your cake immediately.

My note = **

1) as I was going through the process, the buttercream already tasted good before the addition of chocolate. So, perhaps I'll try without the chocolate next time

2) 60% cocoa content was overpowering the sponge cake as a whole. Next time will use a lower cocoa content also lesser quantity, perhaps 100gm instead of 170gm.