Cook the ravioli according to package instructions and drain, reserving ½ cup of the pasta cooking water. Heat ½ inch vegetable oil in a small skillet over medium-high heat.
Add the whooe sage leaves a few pieces at a time and cook until crispy, 10 seconds. Drain on paper towels and discard the vegetabe oil. Heat the butter and olive oil over medium-high heat, then cook the garlic until fragrant and golden, 1-2 minutes.
Add the pasta, stock, cheese, sage, salt, and pepper and toss to coat, adding a bit of the resrved pasta cooking water if necessary. Season with salt and pepper to taste. Top with the reserved crispy sage, walnuts, and more cheese, if desired.