Adapted from "Forgotten Skills of Cooking" by Darina Allen
1Set a heavy medium-size saucepan with tightfitting lid over medium-low heat. When the pan is hot, add 2 tablespoons of the butter. When the butter starts to foam, add the onion, season with salt and pepper, cover, and cook over low heat for 5 to 10 minutes, until the onion is translucent and soft but not colored. Remove from heat; keep warm.
2Meanwhile, heat a large frying pan over medium-high heat until hot, about 2 minutes. Add 1 tablespoon of the butter and cook until foaming. Add half of the mushrooms and season with salt, pepper, and 1/2 teaspoon lemon juice. Sauté, stirring occasionally, until mushrooms are browned on both sides, about 2 to 3 minutes. Transfer to a medium bowl. Repeat with remaining butter and mushrooms.
3Add mushrooms and cream to the cooked onions and bring to a simmer over medium heat until the flavors meld, about 2 to 3 minutes. Add parsley and chives, if using, and stir to combine. Taste and add salt, pepper, or lemon juice as needed. The sauce can be refrigerated for up to 5 days or frozen for up to a month.
Finding the absolute best ingredients such a big part of Chef Antoine Westermann’s culinary career and the main drive behind all of his expertly crafted dishes. His relationship with farmers and purveyors are critical to his work as a chef. While visiting one of his providers in New York, the French chef describes his efforts to find the best local ingredients for his restaurant.