Bring a large pot of generously salted water to a boil. Cook the refrigerated ravioli according to the package directions, usually 3–5 minutes, and reserve about 1/2 cup of the cooking water before draining.

Toast the roughly chopped walnuts in a large skillet over medium heat for 2–3 minutes, stirring frequently. Transfer the fragrant walnuts to a plate so they do not continue browning in the skillet.

Add the butter to the skillet over medium heat. When it foams, add the sage and garlic, then cook for approximately 3–5 minutes, swirling the pan, until the milk solids are golden brown and the butter smells nutty.

Add the baby spinach and toss for 1–2 minutes, just until wilted. Season with the kosher salt and freshly ground black pepper.

Add the drained ravioli to the skillet and toss gently with the brown butter and spinach. Add 2–4 tablespoons of reserved pasta water to loosen the sauce and help it coat the ravioli.

Remove the skillet from the heat, then add the Parmesan, toasted walnuts, and optional lemon juice. Toss carefully so the ravioli stay intact.

Serve immediately with additional Parmesan, black pepper, and a few extra walnuts or sage leaves. Spoon any remaining brown butter and spinach from the skillet over the top.