Snap off the ends of the asparagus, or trim off any woody texture at the base. Meanwhile, heat a griddle pan over a high heat, then add the asparagus in batches. Cook for 3-4 minutes on each side, until the asparagus is lightly charred and tender.
Transfer to a serving dish and add the butter. Toss well to coat and season with salt and lots of black pepper. Squeeze over the lemon juice, just before serving.