How to thicken buttercream without adding more sugar I made some buttercream frosting for brownies using this recipe.  Because The frosting is going on brownies, it needs to be thicker than what it would be on something like a cupcake.  We typically frost the entire pan of brownies and then cut the brownies into bite sized squares.

But this recipe comes out thinner than I would like for the brownies.  Our usual recipe calls for twice the amount of sugar, but that makes it really sweet.  With this recipe, the sweetness is overpowering.

Is there anything else that I can use to thicken the frosting without making it overly sweet?
It looks like a couple of similar recipes in your link there, but you could make it a teensy bit thicker without increasing the sweetness by 1) diminishing slightly the amount of liqueur, or 2) adding a little bit of unsweetened cocoa powder [but of course it will then become brown and chocolatey], or 3) adding a little more cornstarch [since confectioners sugar does contain cornstarch anyway]... or some combination of above.  Go easy at first of course.