Wash the greens and set them aside. Bring a pan of water to the boil, salt it lightly and cook the greens for no more than a minute or two. They must retain their crispness and vigour. Drain and set aside
Meanwhile, warm the butter and oil in a shallow pan, peel and crush the garlic and soften it in the butter and oil. Add a little grated lemon zest (a couple of teaspoons should suffice), then, as the butter starts to froth, squeeze in the lemon juice.
Lower in the greens and toss them gently in the hot, lemony garlic butter. Correct the seasoning and serve immediately.