Peel the artichokes as best you can (they are knobbly and not the easiest of things to peel) then place them in a steamer basket or colander over a pan of hot water, cover tightly with a lid and steam for 10–15 minutes till tender to the point of a knife.
Remove from the heat and halve each artichoke lengthways. Warm the butter and oil in a shallow pan over a moderate heat. As it starts to bubble, add the artichokes, cut side down, and leave for 5–6 minutes to brown lightly.
Meanwhile, chop the parsley and finely grate the lemon zest. Turn the artichokes onto their backs, let them cook for a few minutes longer, then add the parsley and lemon, and a grinding of salt and black pepper.