Lamb Roast

Well, it's Sunday afternoon, and it's stinking hot. Not weather for toiling over a hot stove. So I've done a very Australian thing, and I'm cooking a lamb roast.
When my mum makes a lamb roast, it's very simple. Slather the roast in whole grain mustard, stick in a baking tray (add onions if feeling creative). In another tray, add big chunky pieces of carrots, potato, pumpkin, sweet potato and maybe another onion. The vegies are drizzled with olive oil, and cracked black pepper. Cook until done.
If we were lucky, we'd get gravy - mum's gravy was always thick and yummy. I try to replicate it sometimes, but it's tricky. Her recipe involved heating the juices in the roasting tray on the stove top, simmered with added water. Soy sauce, worcestershire sauce, tomato sauce or whatever else was close at hand would be added in judicious amounts. And often it would be thickened with cornstarch at the end. This whole feast was inevitably served with minty boiled peas.
My roasts aren't much different, but I experiment. Today's roast has slivers of garlic stuck into it (thankyou, Gabriel Gate, for that idea) and was brushed with a mix of rosemary and olive oil. I cook my roast on a rack - which i've never seen Mum do. And my vegetables include whole cloves of garlic and quartered beetroots. I've done more asian style flavours, and sometimes middle eastern with harrisa and lemon, but today i just felt like an old-fashioned lamb roast.