This is a very basic recipe in which you can subsitute other greens like spinach or mustards for the kale as well as onions for the leeks.  Try it for breakfast with your eggs and toast! 

Butter or cooking oil
Leeks (or onions), cleaned and finely sliced
Kale, tough midrib removed and chopped
Bacon, several slices, chopped

Cook bacon until crisp and reserve.  In large pot, sauté leeks in oil gently until tender, 5-10 minutes.  Add kale to leeks, put a lid and a little water and cook until wilted.  Add bacon and drippings, mix and season with salt and pepper to taste.