Preheat oven to 350 F and prepare a large glass baking dish by drizzling a little oil on the bottom.
Melt the butter in a skillet, and saute the carrots, garlic, and onion for about 2 minutes.
Add about 1 tablespoon of lemon juice, and a pinch of the lemon zest, along with the pork tenderloins. Brown the tenderloins thoroughly on all sides for about 5 to 7 minutes.
Transfer the tenderloins to the baking dish and roast for about 30 minutes.
Make the sauce as they roast. Without cleaning the skillet, add the remaining lemon juice and zest, wine, and time, stirring in the vegetables, garlic, and any scrapings from the meat.
Allow the sauce to simmer for 2 minutes, seasoning to taste with salt and pepper.
Once the tenderloin has roasted for 30 minutes, remove from the oven, and add to the skillet again, turning to coat with the sauce.
Continue to simmer for another 5 to 10 minutes. The tenderloins should still be a little bit pink on the inside.
Remove the tenderloins and transfer to a serving dish.
Add the butter to the skillet, and whisk in the heavy cream. Allow the sauce to cook for 2 to 3 minutes.
Slice the tenderloin into medallions, and drizzle the sauce over them to serve.