Place butter in a mixing bowl and add chopped mushrooms, shallots, wine and salt. Blend all ingredients together on low speed until well combined. Transfer butter mixture to a sheet of parchment paper. Fold paper over and roll into a cylinder, twisting the ends. Wrap cylinder in plastic wrap and hold in fridge until solid. Butter will keep refrigerated for up to 2 weeks or frozen for up to 3 months.
To use, cut butter into coins. Butter can be added to pan sauces or to the tops of grilled steaks. Butter at room temperature can also be used as a spread on toast.