• Salt
• ½ cup plus 6 tablespoons unsalted butter
• 3 cups sliced red onions, about ¼ inch thick
• ¼ cup olive oil or as needed
• 1½ pounds calves liver, cut into eight ⅓-inch-thick slices
• freshly ground pepper
• 1⅓ cups Chicken Stock
• ½ cup Dijon and/or Square One Hot Mustard
• Black Pepper Pasta dough for 4 servings, cut for fettuccine or pappardelle

Heat a large pot of salted water to boiling for pasta.

Heat ½ cup butter in a large sauté pan over medium heat. Add the onions and cook until tender, about 5 minutes; remove from the pan and set aside.

Heat ¼ cup oil in the same pan over high heat. Lightly sprinkle the liver with salt and pepper. Put as many slices as will comfortably fit in the pan and sear 2 minutes each side for medium-rare; remove from the pan and keep warm. Repeat with the remaining liver, adding more oil if needed.

Pour off the excess oil, add the stock to the pan and boil, scraping up the browned bits on the bottom, until slightly thickened, about 2 minutes. Return the onions to the pan, add the mustard, and cook, stirring constantly, 1 minute. Season to taste with salt and pepper. Return the liver to the pan and heat through.

Meanwhile, cook the pasta in the boiling salted water just until tender. Drain and toss with the remaining 6 tablespoons butter.

Arrange 2 slices of liver on each serving plate. Spoon the onion mixture over top and serve with the pasta.