Step 1 Put potatoes in a large saucepan, cover with cold water and bring to the boil. Cook potatoes, uncovered, for 10 minutes, or until just tender; drain well. Crush potatoes lightly with a potato masher.
Step 2 Meanwhile, brush Dijon mustard around edges of fillet steaks, then wrap 2 pieces of prosciutto around steak edges, securing overlapping prosciutto to beef with a toothpick.
Step 3 Oil the grill plate and hotplate of a barbecue; heat to medium–high. Cook crushed potatoes on hotplate, turning, for 10 minutes, or until crisp and golden. At the same time, cook steaks on grill plate for 2–3 minutes per side, or until done to your liking; leave to rest. Cook asparagus and tomatoes on hotplate for 5 minutes, or until tender and lightly charred.
Step 4 Make gravy according to sachet instructions. Remove all toothpicks from cooked steaks; discard. Serve prosciutto-wrapped mustard beef with a small jug of gravy, crushed potatoes, asparagus and tomatoes.