Season the tenderloin with salt and pepper. Heat a large skillet over medium-high heat. Once hot add 2 tablespoons butter or oil. When the butter subsides from foaming, add meat to the skillet. Brown well on all sides, about 4-6 minutes. Turn off the heat, remove the meat to a cutting board and let rest. Once the skillet has cooled off proceed to step 2.
Cut meat into 1-inch slices. Reheat the skillet on medium-high heat. Add the remaining butter, add the pork medallions to pan. Brown on both sides, about 2-3 minutes each. Turn the heat down to low, remove the meat to a serving platter.
Add 1/2 cup water to the skillet, turn heat to high, and cook, stirring for about 1 minutes. Lower the heat and add in the remaining ingredients. Taste and adjust the seasoning if needed. Serve the pork medallions with the pan sauce spooned over the top.