Preheat the oven to 400°F and allow the pork to stand at room temperature for 30 minutes.
In a small bowl, mix the olive oil, Dijon and whole grain mustards, garlic, rosemary, salt, and pepper. Rub this mixture generously over the pork. Place the pork in a cast-iron pan.
Roast the pork for about 75 minutes, or until a thermometer inserted into the thickest part reads 145°F. Once done, remove the pork from the pan and transfer it to a cutting board. Tent with foil and let it rest for 10–15 minutes.
Leave about 1/4 cup of drippings in the same cast-iron pan, discarding any excess.
Set the pan over medium heat and whisk in the flour, letting it cook for 1 minute. Pour in the white wine, allowing it to cook and bubble until slightly reduced.
Gradually add a bit of chicken stock, whisking as you go. If more space is needed, transfer to a larger pot and add the remaining chicken stock, up to 2 cups total.
Stir in the mustard and rosemary, and adjust the seasoning if needed. Let the sauce simmer for 5 minutes, reducing and thickening. Add more chicken stock for a thinner sauce until it reaches your desired consistency.
Carve the pork between the bones and serve with the warm sauce on the side. Enjoy!