This finely chopped mushroom mixture sautéed with butter and herbs is a traditional French preparation used in many sauce and stuffing recipes. It’s said to have been invented by the 17th-century French chef François Pierre La Varenne, who supposedly named it for his employer Nicolas Chalon du Blé, marquis d'Uxelles. You can use most any kinds of common mushrooms depending on the flavor you’re looking for.
Finely chop the mushroom caps and stems until they look like confetti (or pulse in a food processor). Warm the oil and butter in a sauté pan over low heat. Add the shallots and simmer until translucent. Then, add the mushrooms and thyme. Season with salt and pepper, to taste. Cook until the mixture is soft and the moisture has evaporated, stirring frequently, for about 10 minutes.