From The Enchanted Broccoli Forest, by Molly Katzen
1/2 lb Brussels sprouts
1/2 cup chopped onion
1/2 lb chopped mushrooms
2 Tbsp butter
1/4 tsp salt
lots of freshly ground black pepper
1/2 tsp dill weed
1/2 tsp dried tarragon
1/2 tsp dry mustard
1 cup hot milk
1/2 tsp prepared horseradish
1 packed cup grated cheddar
Cut the Brussels sprouts into quarters, and put them up to steam for 10-15 minutes.
Cook the mushrooms and onions together in butter, with salt, until the onions are soft (8-10 minutes over medium-low heat). Add herbs as they cook.
Sprinkle in the flour, stirring as your sprinkle. Cook a few minutes more, stirring.
Gradually drizzle in the hot milk. Stir with a wooden spoon. Cover, and cook over very low heat- stirring intermittently- for 5-8 minutes. Stir in the horseradish, the cooked Brussels sprouts, and the cheese. Set aside while you cook your pasta (about 1/2 lb for this amount of sauce).