When I make my leek and potato soup, the recipe calls for cutting off the leek just above the bulb as you mention, DramaQueen. I don't do that anymore though. I cut quite a ways into the green. After I've sliced the leeks, and washed them, I sautee them in a little bit of light olive oil - and proceed with the rest of the recipe. At the end, since everything is pureed, you don't notice any toughness. I've also added this part of the leek (if it doesn't look grungy) to vegetable stock.