Pasta with Swiss Chard and Leek Sauce

What can you do with your CSA swiss chard, leeks and scallions? Turn them into a sauce! This sauce goes exceptionally well with wild mushroom and truffle ravioli. If you live in Brooklyn, try the fresh raviolis from Union Market. They are pricey, but worth it.
The combination of swiss chard and leeks is terrific. Shout out to Kathryn who suggested the combination after she modified a Smitten Kitchen post.
The sauce, which is thickened by a roux (a mixture that is traditionally a combination of flour and butter), is easy to make. It's also delicious! I may even make it again this weekend...but that would make three times in two weeks. I guess that's a bit excessive.

Swiss Chard and Leek Sauce
1 bunch Swiss chard, thick stems removed and leaves sliced into ribbons
2 leeks
1 scallion
3 tablespoons butter
3 tablespoons all-purpose flour
1 3/4 cups milk
1/8 cup of grated parmesan
Salt and pepper

Making the roux: butter, chard, leeks, flour and milk.

Preparation

Wash your chard (no need to dry it). Fill a large fry pan with water-- enough to cover the swiss chard leaves. Place the leaves in the pan and cook uncovered over a medium heat. Stir occasionally, until wilted, about 6 minutes.
Remove the chard from the pan and press out the excess liquid. (I used a cheesecloth.)
Heat the milk in a small saucepan over moderate heat, stirring, until warm. Keep warm.
Meanwhile, put 3 tablespoons of butter in the pan that once had the chard. Heat on a moderately low flame. When the butter is melted, add the leeks and scallions. Stir occasionally, until softened, about 6 minutes. Whisk in flour and cook about 3 minutes. Slowly add warm milk, whisking constantly to prevent lumps. Whisk until thickened, 3 to 4 minutes. Stir in chard, then salt and pepper to taste and cook, stirring, until heated through. Add 1/8 cup finely grated parmesan to the roux while it is being cooked.  Pair this with your favorite pasta (I went with mushroom ravioli). Dinner is served!