There's richness, and then there's richness. Many a sauce promises a velvet touch, but this one delivers and in spades. The acid of wine mixes with the pungent delight of mustard and the rich depth of the demi-glace. Butter swirled in off-burner levels up the richness, bringing you to the stars and back in pure gastronomic goodness. You'll never eat a steak without sauce after this. Tip: This recipe contains shallot, which, while delicious, is a small vegetable and sometimes difficult to mince. Best practice is to make thin slices lengthwise, then slices across, resulting in a minced shallot with little stress.