Lentils with smoked gouda

This is a Pendle Hill recipe that's become one of my staples. Lentils cook faster than most beans even without soaking, so this dinner can be done about an hour after you get home.

Rinse 3 cups French lentils (also called lentils du puy. They are dark green in color and are much nicer than red or brown lentils.)
Cover with plenty of water and boil until tender.

Turn on the oven to 350. Drain the lentils and stir in:

1 teaspoon sage
Salt to taste
Broth or broth powder

Other possible additions:
a dash of vinegar
mustard
chopped apple
chopped walnuts
cooked sausage

Put in a greased casserole and top with grated cheddar or smoked gouda. Bake until the cheese is bubbly.