Add butter to a skillet over medium-high heat. When the butter starts to foam, add the mushrooms.
Sprinkle kosher salt over the mushrooms and saute until the mushrooms' water is released and cooked off, about 5 to 7 minutes.
Add the shallots, garlic, and Herb and Spice Blend; mix well and sauté until the shallots start to turn translucent, about 3 minutes.
Add the chicken stock and simmer until reduced by about half
Add the heavy cream. When you see bubbles around the edge, reduce the heat to medium and simmer until starting to thicken, about 5 minutes. The cream should coat the back of a spoon without running.
Add the creole mustard and mix well.
Simmer for 3 to 5 minutes, then serve.
Notes
Refer to my article, Creole Mushroom Sauce, for more step-by-step instructions with photos, Ingredient Notes, Substitutions, and more tips on creating a great sauce.This recipe makes about 1 ½ cups of sauce. A serving for nutritional purposes is 3 ounces. This recipe can be doubled easily. You can substitute any type of mushroom you like. Vegetable stock is a suitable substitution for chicken stock in this recipe.Leftover sauce will maintain its quality for 3 to 4 days in the fridge and up to 2 months in the freezer, if stored properly. Refer to this article for more details on leftover storage and handling.