Preheat your oven to 220°C/200°C fan/gas mark 7.
Remove the lamb steaks from your fridge to allow them to come up to room temperature. Bring a large saucepan of water with 1/2 tsp salt to the boil for the potatoes.
Peel and chop the potatoes into 2cm chunks. Finely chop the walnuts. Peel and grate the garlic (or use a garlic press).
When boiling, add the potatoes to the water and cook until you can easily slip a knife through, 15-20 mins.

Put the panko breadcrumbs, walnuts and dried rosemary onto a plate and drizzle with the olive oil for the crumb (see pantry for amount). Season with salt and pepper, then stir together well.
Season the lamb steaks, then evenly spread half the Dijon mustard all over each.
Press the steaks into the crumbs, making sure they're well coated on each side. IMPORTANT: Wash your hands and equipment after handling raw meat.

Heat a drizzle of oil in a large frying pan on medium-high heat.
Once hot, carefully lay in the crumbed lamb steaks. Fry until golden, 2 mins each side, then transfer to a baking tray.
Roast on the top shelf of your oven for 5 mins for medium-rare. TIP: Cook for a few more mins if you prefer yours more well done.

Once the potatoes are cooked, drain in a colander and return to the pan, off the heat.
Add the butter (see pantry for amount), cheese and a splash of milk (if you have any) and mash until smooth.
Season with salt and pepper. Cover with a lid to keep warm.

Once the lamb is cooked, remove from your oven and leave to rest on a board for a couple of mins.
Wipe out the frying pan, then pop back on medium-high heat.
Once hot, add the spinach and season with salt and pepper. Stir together and cook until wilted, 1-2 mins.
Stir in the garlic and cook for 1 min more, then stir in the creme fraiche and cook until piping hot. Taste and season if needed, then remove from the heat.

When everything's ready, transfer the lamb steaks to your plates.
Serve the spinach and mash alongside with any remaining Dijon mustard.
Enjoy!