In a small bowl, whisk together flour, garlic powder and onion powder, and season generously with salt and pepper.
Slice pork tenderloin into medallions. Dredge tenderloin slices thoroughly in dry mixture, pressing gently so it adheres, then heat 2 Tbsp. butter in a large skillet over medium-high heat.
Once hot, add tenderloin and cook, without moving (other than to flip) until tenderloin is browned on both sides.
Remove pork from heat and transfer to plate. Cover to keep warm.
Return skillet to heat and pour in wine, lemon juice and zest, minced garlic, and thyme, and then season again with salt and pepper.
Reduce heat to medium and stir everything together, making sure to scrape up the browned bits at the bottom of the pan. Return tenderloin to pan, reduce heat to low, and simmer 15-20 minutes or until tenderloin is cooked through.
Remove tenderloin to plate (or 200° oven), then add remaining butter to sauce in skillet. Whisk in heavy cream and bring to a boil, then reduce heat to low again and simmer until thickened.
Once desired thickness is reached, drizzle sauce over the tenderloin and serve hot.