Whisk together the ½ the Keen’s Mustard Powder, flour, eggs, chives and milk. Allow batter to rest.
Sprinkle the beef fillet with salt and pepper and then rub with remaining mustard and 1 tbsp of olive oil.
Place beef in a medium (180oC) oven for 50-60 minutes or cook to your liking and let rest while cooking puddings.
Divide left over oil into 6 muffin pans and place in a hot (230oC) oven for 10 minutes until oil is smoking. Fill muffin cups ½ way up with batter and return to the hot oven for a further 15 - 20 minutes.
Serve sliced beef with Yorkshire puddings filled with gravy.
Tip: Add 2 tsp of mustard powder to your gravy mix for an extra hit.