1 1/2 pounds pork tenderloin, cut into 1-inch-thick medallions
4 tablespoons butter
1 cup chicken stock or canned broth
1/4 cup fresh lemon juice
2 tablespoons capers, drained
1/4 cup peeled diced lemon segments (optional)
Chopped fresh chives or green onion tops
Press pepper onto both sides of pork pieces. Heat 1 tablespoon butter in heavy large skillet over medium heat. Season pork with salt. Cook until just cooked through, about 4 minutes per side. Transfer to plates and keep warm.
Add stock and lemon juice to skillet. Boil until reduced to 1/2 cup, about 7 minutes. Whisk in remaining 3 tablespoons butter. Add capers and lemon segments if desired. Season to taste with salt and pepper. Pour sauce over pork. Sprinkle with chives and serve.