By Butterhorns I suppose you may mean what I know under the term "Vanillekipferl" (you can take a look at http://www.vanillekipferl.com). This is the traditional recipe my family uses - you'd have to convert the measurements:

200g(gramm) butter
250g flour
125g ground nuts (one half almonds, the other walnuts)
70g powdered sugar
1 teaspoon vanilla sugar

Knead everything together, cover it up and let it sit for some time.

Then form horns by rolling small strings from the dough and bending them.
Bake for about 10 Minutes (until the ends start getting a bit dark) at 180° (about 350 °F).
Let them cool a bit, then roll in powdered sugar mixed with some vanilla sugar. Be careful they break easily