Another dish that somehow transcends the sum of its parts — with every bite you will wonder how steak, vegetables and mustard could synthesize into something so eye-rollingly delicious. Extra points for coming together quickly and even more for adaptability: several commenters used different cuts of meat and one even substituted chicken; I kept thinking how lovely it would be with a tuna steak.
As written the mustard sauce was far more than needed so you can either make less or save it for something else later in the week (eggs?). I was too cautious with the cayenne (one stingy pinch) so if you’re really looking for a kick two generous pinches should get you there.
Cooks illustrated.