I used a recipe from Short-Cut Vegetarian by Lorna Sass as a guide. The recipe calls for leeks to be cooked in olive oil, then for cubed potato, Dijon mustard, water, salt, and vegetable stock powder to be added. Cabbage is added later, and the dish is finished with pepper.
I opted for different proportions of leek and potato than the recipe recommended (more leek, less potato). I also added extra mustard. I can see why the author recommended red-skinned potatoes, as the dish is rather bland in appearance, but I was unable to find them. I also added a bit of minced garlic to the leeks.