3
Add the onion and celery to a food processor and process until they are very finely chopped, almost at a chunky paste. Remove from the food processor and set aside. Then, add the toasted nuts, garlic, nutritional yeast, rosemary, thyme, paprika, sage, and black pepper to the food processor. Pulse until the nuts are very finely chopped, almost resembling coarse breadcrumbs. Reserve 3 tablespoons of this mixture to top the mushrooms; place the rest in a separate bowl apart from the onions/celery.