After pan-cooking steaks or other meat, turn the heat down to medium and remove all but one tablespoon of fat. If there is none, add a tablespoon of butter.
Add the minced shallots and cook, constantly stirring until softened. About 1 minute.
Add 1 tablespoon of butter and add the flour. Continue cooking, stirring constantly for about 30 seconds.
Slowly add the stock, the wine, and the mustard. Stir the sauce, scraping off the browned bits off the bottom of the pan with the spoon.
Bump up the heat to high and let the sauce simmer until reduced to 1 cup, about 5 minutes.
Remove the pan from heat and add the parsley, lemon juice, and the remaining 3 tablespoons butter and whisk until all ingredients are well combined.
Season with salt and pepper to taste and serve with red meat.