To make the browned butter sauce, heat a skillet on medium heat, add in all of the butter and let it melt. Stir melted butter around and add in the sage leaves, tearing about half of them into smaller pieces. The leaves will begin to fry.
Add in the walnuts, salt, and pepper. Continue stirring and when the sage and butter have both browned, add in the ½ cup of pasta water. This should create a nice consistency to coat the ravioli with.