Leeks are far better. They have a softer, less slippery texture, and a milder taste. Onion and Stilton could prove a bit overpowering.
EASY LEEK AND POTATO SOUP
When cooking a big dinner keep all the vegetable stock. Reduce it down if necessary.
Next day use it for soup. Throw in chopped leek and small chunks of potato. Season with salt and pepper. Proportion of leek to potato is a matter of taste. Allow the potato to break down to thicken the soup. Add a large knob of butter. If it is pondweed green and you want to freshen up the colour add a quarter of a teaspoon of turmeric. Add chopped fresh parsley before serving. True gluttons can stir in a bit of cream, but it's not really needed if you have added butter. Very nice with bread and cheese.