In a large skillet, heat 1 tablespoon of the butter over medium-high heat. Add the pork and brown quickly on all sides, about 2 minutes total.
Reduce heat to low, remove pan from heat and gradually add 1/2 cup water. Cover pan and return to heat. Cook 15 to 20 minutes, or until pork registers 145 degrees F on an instant-read thermometer. Remove pork; keep warm. Drain drippings into a 1-cup measure. Set aside.
In same skillet, melt remaining tablespoon butter over medium heat. Add scallion, celery and garlic. Cook 4 minutes, stirring, until tender.
In a small bowl, stir together cornstarch, ginger, pepper, salt, thyme and 1/4 cup water. Return pan drippings and cornstarch mixture to skillet, stirring until smooth. Cook 2 minutes, or until thickened. Slice pork; serve with gravy. Makes 2 to 3 servings.