Preheat oven to 350 F (180 C). If you have a convection oven, use that setting.
To prepare rosemary pork loin, remove the excess fat and the silver skin from the meat. Peel the carrots and cut garlic heads in half lengthwise.
Oil the bottom of a 9x13 baking dish. Put the carrots, garlic heads and 4-5 fresh rosemary sprigs into the baking dish. Pour in 1/4 cup of white wine and the same amount of water.
Season the meat with salt and freshly ground black pepper. Place it over the vegetables and top it with the remaining rosemary springs.
Put it in the oven and bake uncovered for 90 minutes. Baste it with the cooking liquids after 30, 60 and 75 minutes. Once your meat is cooked, take it out of the oven and let it rest for 10 minutes covered with an aluminum foil.
Rosemary gravy
For your rosemary gravy, take out the carrots, garlic, and rosemary from the baking tray. Place it on your stove on low heat. Add flour, mix it with the drippings and cook for 1-2 minutes.
Pour in ½ cup of white wine. Stir it to remove any lumps and cook for another 2 minutes to let the alcohol evaporate.
Pour in 1/2 cup water and add 1 rosemary sprig. Stir and cook for 2 minutes, so that it thickens up. Taste and season with salt if needed.
Remove from the heat and add the butter. Stir until it melts completely.