Pork Tenderloin with Balsamic Mushroom Sauce

I made one of my infrequent trips to Costco last weekend and bought a bunch of great things. Toilet paper for the rest of my life. A new Brita (so exciting). Crab meat. And a large portion of pork tenderloin...more than I orginally had thought. I browned the pork on the stovetop first...I could have browned longer, I was just impatient. Then poured some of the earlier sauteed onions and mushrooms over the meat before sticking it in the oven to cook.
I combined the remaining mushrooms and their juices with a little sour cream to make a saucy sauce.
This dish grew on me as the days went by, I think that the flavors improved after the initial out of the oven reveal.