Preheat oven to 350 degrees F. Line a shallow baking pan with heavy-duty foil.
Mix the 1 tsp garlic powder, 1/2 tsp salt and 1/4 tsp of pepper and rub on the pork loin. Place the pork loin in the prepared pan and roast, uncovered, for 50 minutes.
For the sauce, melt the 1 tbs butter in a small saucepan. Add the onion and cook until the onion is soft but not brown. Mix in the remaining sauce ingredients. Bring to a boil, then reduce heat to low and simmer for 20-25 minutes or until reduced to about 3/4 cup.
Brush the sauce over the pork and cook for 15-20 minutes longer or until the internal temperature reaches 145 degrees F. Remove from the oven to a platter.
Tent the roast with foil and let the roast stand for 10 minutes before slicing
* This is a great place to use one of those mustard packets you get with take-out. If you don’t have one, mix an equal amount of water and dry mustard powder until smooth. Let it stand for about 10 minutes before using.