Let the pork rest on the counter for about 30 - 60 minutes before patting it dry and seasoning both sides with salt and pepper
In a cast iron or stainless steel skillet, heat the oil over medium to medium-high heat
Sear the pork for 4 minutes on one side, about 3 on the other and then using tongs, sear all sides of the pork for about a minute
Next, reduce the heat to medium and add 1 T of butter and the rosemary sprigs tilting the pan allowing you to fill a spoon and constantly baste the pork
Continue basting until the pork's internal temperature is 135 degrees. Add some of the stock to discourage any burning or drying out of the pork as the butter dwindles and you arrive at the 135 mark
Remove the pork to a plate to let it rest and in the same pan add the last T of butter, garlic, shallot, vinegar, 1/2 C of stock, and both mustards stirring for a few minutes until it all comes together
Lastly, add the cream and any pork juices from the resting plate and stir until thickened. Less cream will keep the sauce tight with strong flavors, adding more cream will create a creamier sauce with more subdued flavors
