Bring a large pot of well salted water to a boil. Cook the ravioli to just below al dente according to package instructions. It will cook a bit more in the butter sauce, so leave yourself some wiggle room.

While the water boils, place the walnuts in a wide, dry skillet (I like stainless steal, ceramic, or another light-colored skillet for this recipe because it's later to watch the butter brown later on). Heat over medium heat, stirring often, until the walnuts smell toasty, about 3 to 5 minutes. DO NOT WALK AWAY. I'm telling you, nuts love to burn. Immediately transfer to a bowl to stop their cooking.

With a paper towel, carefully wipe out any remaining walnut "dust." Set a paper towel-lined plate near the stove.

Cut the butter into 4 pieces. Add to the skillet and heat over medium-high heat. Once the butter is almost melted, add the sage leaves and cook for 1 to 2 minutes, until they are crisp. With a slotted spoon, transfer the sage to the paper towel-lined plate.

Grab a whisk. Continue heating the butter, whisking constantly to scrape up the toasty brown bits that will start collecting on the bottom. Be careful, the butter spatters. As soon as the butter smells nutty and some of the solids are the color of a pecan, remove it from the heat.

Whisk in the salt and cider vinegar (the butter will sizzle and hiss).

With a handled mesh strainer or spider (or a large slotted spoon) scoop the ravioli from the boiling water right into the skillet, gently shaking each spoonful so you don't flood the butter with pasta water. Don't worry if some of the water is clinging to it, this will actually help with the sauce. Gently stir to coat the ravioli with the butter, then sprinkle with the Parmesan, walnuts, and fried sage. Serve immediately, with additional Parmesan to taste.