Don't ever walk away from a warm pot unless you know someone else will look after it for you.
While I was cooking this roast, I was called away to rescue a bee swarm. I put it on top of the fennel, switched off all stove burners and went. When I came back much later than I had expected, the roast was steamed instead of roasted; but what was worse, it was also borderline overcooked. The heat in the fennel was enough to cook that roast all the way through. :-( It was still OK to eat, but I prefer lamb’s meat clearly pink to reddish.
This is what you need for 4 servings: