Heat the butter in a large skillet and sauté the breadcrumbs for a few minutes, until lightly golden and fragrant. Pour the breadcrumbs in a bowl and set aside; when cold add thyme leaves, grated Parmigiano, salt and pepper and mix well.
Cook Tortelloni according to package instructions and drain, reserving ¼ cup of the pasta cooking water. In the meantime, heat crème fraiche in a large skillet over medium heat. Add pasta to the skillet, season with salt and pepper to taste and toss to combine adding a little of the pasta cooking water to loosen the sauce if needed.
Divide Tortelloni among 2 plates, sprinkle with celery and breadcrumbs mix and serve.