Heat the Dutch oven over high heat. Add the bacon fat. When the fat shimmers, add the tenderloins and allow them to brown for 3-4 minutes without moving them. If you move them too much, the garlic paste will fall out. Using tongs, flip the tenderloins and cook for another 3-4 minutes. When they are browned, remove them from the Dutch oven and set aside.
Reduce the heat to medium-high. Add the olive oil and the onions, with a pinch of salt. Let the onions cook for 1-2 minutes, stirring well and scraping the browned bits off the bottom of the pot. Add the carrots and celery. Allow to cook, stirring occasionally, for another 6-8 minutes.
Add the dried herbs and mix well.
Add the red wine. Turn the heat to high. Allow to almost completely cook off.
Add the diced tomatoes. Stir well to combine, and turn off the heat.
Add the browned pork tenderloins back into the pot, right on top of the veggies.
Cover with the lid and place in the preheated oven for about 1 hour, or until a meat thermometer reads 135°F (57°C).
When you remove them from the hot oven, pull the baked pork tenderloins from the Dutch oven to a cutting board. Cover with foil and set aside to let the meat rest for 10 minutes, then slice against the grain into about ½ inch slices.
Remove the veggies from the Dutch oven and add to a serving dish. Layer the sliced pork over the veggies and serve hot. Enjoy!