Flavored with white wine, mustard, onion, and sliced cornichons, this tangy sauce pairs well with sautéed pork dishes because it cuts through their richness. Charcutière sauce, a popular staple at Parisian bistros, is even more delicious when made in the skillet used for sautéing the pork because the caramelized juices from the bottom of the pan boost the sauce's flavor and color.
6 tbsp. extra-virgin olive oil
12 1⁄2˝-thick slices pork tenderloin
Kosher salt and freshly ground black pepper, to taste
1⁄2 small onion, finely chopped
1 cup white wine
2 tbsp. chilled unsalted butter, diced
1 tbsp. dijon mustard
6 cornichons, julienned
1. Sear the pork: Heat 2 tbsp. oil in a 12" skillet over medium-high heat. Rub pork with 2 tbsp. oil; season with salt and pepper. Add half the pork to skillet; cook, flipping once, until lightly browned and just cooked through, about 5 minutes total. Divide pork between 2 plates, overlapping 3 pieces on each plate. Repeat with remaining olive oil and pork. Cover plates loosely with foil; set aside in a warm place to let rest while you finish the sauce.
2. Make the sauce: Return skillet, with brown bits from pork still in it, to medium-high heat. Add onions; cook, stirring and scraping occasionally with a wooden spoon, until onions begin to brown, about 3 minutes. Add wine; simmer until reduced to about one-fourth its original volume, about 5 minutes. Add demi-glace; whisk in butter until smooth. Remove skillet from heat; stir in mustard and cornichons. Season with salt and pepper. Spoon 2–3 tbsp. sauce over pork. Garnish plates with sautéed sliced red cabbage, if you like. Yields about 3⁄4 cup sauce.