Okay, eggs, butter, and milk are certainly not roughage, but this frittata, which verges on being a crustless quiche, is mostly a tangle of flavorful, if pale, vegetables, with just enough egg to hold them together. If you accompany it with a big green salad, no one should have anything to complain about. The mustard cream, which can be made with creme fraiche, full-fat yogurt, less-fat yogurt, or sour cream, is an idea from Deborah Madison that I find pulls the dish together magnificently. (It's fantastic with asparagus, too, by the way.)
You can prepare the cabbage and leeks ahead and refrigerate for a few days, in which case assembling the final dish is really a snap. It's not too much work for a weeknight, even so. Also, if you dislike cabbage, just substitute another leek or two.
LEEK AND CABBAGE FRITTATA
3 leeks, white and palest green parts only, sliced and washed VERY well
Some of a small green cabbage, core removed and cut to match the leeks, enough to make about 2 cups once sliced.
2 tablespoons unsalted butter
1 teaspoon salt
1/2 cup water
Put all of the above ingredients into a heavy-bottomed pan with a tightly fitting lid and bring to the boil, uncovered, over a medium-high flame. Let boil for five minutes, then turn the heat to very low and cover. Let the vegetables stew for half an hour, until extremely tender (but still as full of fiber as ever they were!). Set aside.
3/4 c milk (preferably whole)
Freshly ground pepper
Splash of olive oil
Beat eggs and milk together. Stir in the vegetables until well mixed. Add pepper. Heat a splash of olive oil in the bottom of a heavy frying pan (I vastly prefer nonstick for eggs) and pour in the egg mixture. Cook over medium-low heat until it begins to set, then finish it up in either a hot oven (say, 400 degrees) or under the broiler.
MUSTARD CREAM SAUCE
3 T very finely minced red onion or shallot
2 t wine or sherry vinegar
Fat pinch salt
1 T prepared mustard
3/4 c full-fat yogurt (see notes above for other options)
Combine minced onion, vinegar, and salt and set aside for at least five minutes. Add mustard and yogurt and mix well.