Cut the potatoes into 50mm thick slices. Slice the carrots and leek too. Cut off the woody ends of the asparagus.
Mix the butter with the chopped dill, garlic and lemon zest.
Lay the potato, leek and carrot slices in a roasting tin. Crumble some of the butter on top, then add the second layer of vegetables. Add more butter, season with salt and pepper, then put the tray in a preheated oven (to 180°C) and bake for 10 minutes. Baste with the jus and turn over the veggies that are too brown. Bake for another 10 minutes.
Meanwhile, rub the asparagus with the remaining butter mixture.
Turn over the veggies again, then lay the asparagus on top of them. Add the lemon juice and bake for another 10 minutes or until tender.
Serve warm.