I'm not usually a big fan of walnuts in baked goods, but this is an exception. I don't care for them (or pecans) in brownies or cookies, but for some reason, pair them with pastry dough, especially if there is cinnamon-sugar involved, and I'm all over it!
2 c flour, sifted
2 sticks, softened
3/4 c sour cream
1/2 t vanilla
3/4 c sugar
3/4 c chopped walnuts
2 t cinnamon
Because I was making this in my food processor (using the dough blade), rather than sifting the flour, I put it in the bowl of the processor by itself first and pulsed it a few times to aerate. Whether doing it by hand, in a stand mixer, or a food processor, start with the flour, then cut in the butter.
Next add the yolk from one of the eggs (you can separate it to leave the white in a bowl for later to go with the egg wash, or just discard that white), the sour cream, and vanilla until the dough comes together and starts to pull away from the sides of the mixer/bowl. It will still be quite soft.
While waiting for your dough to chill, go ahead and chop your walnuts. Some people like to pulse the sugar and cinnamon in their food processor right with the walnuts. For some reason, I always pulse them in the food processor, then stir them into the sugar and cinnamon until evenly distributed.
Now that I'm thinking about it, that would be for measuring purposes. I pulse a bunch of walnuts, then measure out 3/4 c, but it's just for a filling, so it doesn't really need to be exact.
When your dough has chilled and stiffened up, separate it into three sections. If you're quick at this sort of thing, you can leave the rest out, but if you tend to work slowly, you might want to throw the other two pieces back in the fridge so they don't soften up again.
On a lightly-floured work surface, roll out the dough to about a 9" circle, and slice into 8 wedges. I like to use a pizza wheel for things like this. I'll slice it into quarters, then repeat. I sprinkle a little flour on top of the dough as well for this one because it's so soft. Even if I'm putting waxed paper over it, it sometimes sticks to the paper or rolling pin if not floured. Depends on the weather, and it was EXTREMELY hot and humid while I was making these!
It seems as though most people sprinkle the filling over the entire round and roll them in place, but I like to flour a small spatula and remove a wedge, sprinkle the filling, and then roll it. I think they come out cleaner looking that way. I keep the filling more in the center because as you roll them, it will spread out. For the same reason, I stop sprinkling the filling before I get to the tip.
Roll from the wide-end toward the tip and place tip-side down on parchment-lined baking sheet. They will puff up some but won't spread much, so you can keep them relatively close together. Repeat with the other two portions of dough.
Beat the second egg (and reserved white from the first egg if you kept it) with a drizzle of water to create and egg wash and brush lightly over all of the butterhorns.
Bake at between 325°-350° for 25-30" until lightly golden.