Heat grill to a medium-high setting. Cook the bacon under the grill until really crisp, turning halfway through cooking. Remove, drain on kitchen paper and leave to cool.
Put the bacon in a food processor and whizz until finely chopped. Add the butter and some black pepper, and blend again until combined. Transfer to a dish, or roll in cling film and chill for up to 3 days, or freeze for 2 months.
Bring a large pan of salted water to the boil. Add the kale and cook for 3-4 mins until tender. Drain well, then top with half the butter (see tip, below), and toss to help it melt and coat the kale.
Using up surplus bacon butterThis recipe makes double the amount of butter required. Use the remainder on carrots, peas, green beans, on top of white fish, or stuffed under the skin of a roast chicken or turkey.