It never quite stays the same, but the same basic two ingredients do: butter and sage. The butter must be browned and the sage, fresh. Most of the time over these is poured cream, which bubbles into a sauce. But this last, it could be said, just dilutes the flavor.
It was taken from two friends' repertoires, both of whom exalted it.
The one loved gnocchi more than the sauce she bathed them in, but aren't gnocchi a vehicle for sauce? She made gnocchi to bring decadence to our poorly deprived college lives of hippie lentil soup and mac n' cheese. The time-consuming and detailed labor of gnocchi were supposed to bring us out of the fraught, gaudy world of a small New England liberal arts school to somewhere more expansive. Like, say, Italy, after which she pined by kneading dough and smooshing it delicately with a fork.
But the sauce. Her method was to pour some cream into a saucepan with lots of fried sage leaves, simmer it down until it thickened into a sauce, and salt it to taste. This made a sumptuous covering for the pillowy lumps. As such rich sauces are bound to, it drew us all salivating in only to leave us for dead at the table, feeling sick and wanting to collapse into our half-finished plates.
The other was following a recipe for pumpkin ravioli with brown butter and sage, and was enamored, in her self-consciously understated way. She dropped sage leaves into melted butter and burned the butter just so. This is the base, and sometimes the whole, of every permutation of my sauce.
I have a kind of paranoid respect for the flavor of sage and browned butter. I don't think it should be messed with. Olive oil is, I feel, an evil addition to it. Other herbs, even black pepper, should be shunned from sage. Garlic is too much competition, and its cloying, under-your-fingernails savoryness clashes with sage's sharp scent.
The furthest I have strayed from the holy diad has been to incorporate bacon and finely chopped onions. This may have been too far.
I do think that the recipe for pumpkin ravioli had it right: the flavor of sage and browned butter should be paired with something a little sweet. But I rarely do this. I have become more attached to the sauce than its place in a dish. I pour it over any old pasta. Once I even put it on chicken and mashed potatoes.
Once the sage leaves have become brownish and brittle in butter, I often remove them before the cream makes them soggy. These crispy, butter-soaked leaves are hard not to devour on the spot, but I like to sprinkle them as a flavorful garnish.