Slice your pork tenderloin into 8 pieces, about 1 to 1 1/2" each.
Season with the salt, pepper, and garlic powder.
Heat a large, rimmed skillet over medium high heat. When hot, add in 1 tablespoon of butter and the oil.
Sear the pork on both sides, 2-3 minutes per side, and remove to a plate. Set aside.
Turn the heat down to medium and add in the onions, mushrooms, red wine vinegar, and 1 tablespoon of butter with another pinch of salt. Cook until caramelized, 8-10 minutes.
Reduce the heat to medium low. Add garlic with remaining butter. When butter has melted, add the flour and stir constantly for 2 minutes.
Slowly add in the broth, while stirring or whisking, until it's smoothly incorporated. Stir in the Worcestershire sauce and return the pork to the pan.
Return the pan to medium heat and stir occasionally until sauce is thickened to your liking and pork is 145°F.
Taste the sauce and add a pinch of salt or pepper to taste. Serve immediately.
Notes
*Pork tenderloin and pork sirloin/loin are NOT the same. Pork tenderloin in thinner, smaller, and generally more expensive than pork loin. Subbing in pork loin will not give you the same results.