Melt 2 tablespoons butter in a large skillet over medium-high heat. Add sausage and mash with a stiff whisk or potato masher to break up into fine pieces . Cook, stirring frequently, until only a few bits of pink remain, about 8 minutes. Add onion, celery, garlic, and sage and cook, stirring frequently, until vegetables are softened, about 10 minutes. Add parsley and season to taste with salt and pepper. Transfer contents to a large bowl and set aside until completely cool.
