Cut Leek into small dice along with onion. Melt butter in pan,add Leek and Onion. Cook on low gaa for 10 min.. Add flour and mix very well to form a thick paste. Add milk slowly. Stirring continuously, simmer for 10 minutes. Add in Stilton(grated) and stock cube, then liquidize. Stilton is a very strong aged cheese. One could probably substitute real Roquefert or its poor electrically aged cousin Blue Cheese and it still would be wonderful. From Arches Restaurant Edinburgh, Scotland, Chef, George Lawrie