Salt and pepper the tenderloin. Let rest on the counter while preparing other ingredients.
Heat a large skillet over medium heat. When hot, add a drizzle of oil and sear pork on all sides.Transfer to an oven proof baking dish and place in 400 degree oven until internal temperature is 150-155. The cooking time will vary depending on the size of the pork loin. Remove pork to a platter and tent with foil to keep warm and rest before slicing and serving.
In the same skillet, add a bit more oil and a T of butter, Add shallot and cook for a few minutes. Add garlic and thyme and cook a few minutes. Add the white wine to deglaze the pan. Reduce the wine then add the chicken stock, the dijon mustard and the mustard seeds. Cook and reduce sauce. Taste and add more dijon to taste. Add cream and a squeeze of lemon juice. Taste and adjust seasonings to your liking if needed.
Slice pork into 1/2 inch thick slices and serve with sauce and a sparkling of chives. Serves 4-6.