Lentil Croquettes with Caramelized Onion

Now that a study has confirmed that the Mediterranean diet is very healthy (as if we didn't know!), it's nice to have some recipes for legumes such as lentils. One of my favorite meals with lentils is a family recipe, Mujedrah, which is rice and lentils with caramelized onions (the recipe is here). These delicious patties come from Deborah Madison, whose recipes I've shared before, in her cookbook Vegetarian Cooking for Everyone. I like the taste of lentils, but the onions make the dish special. The recipe is fairly simple: cook the onions, cook the lentils, puree the lentils, make the patties, fry them. In her recipe, Madison uses bread crumbs but since my only bread is a homemade sourdough a bit too strongly flavored, I use mashed potatoes; this is a trick I learned from an easy and delicious recipe from Jamie Oliver for salmon cakes, which you can see here. Deborah Madison suggests serving these lentil croquettes with a tomato sauce (she says "even ketchup" but I draw the line against that). I had them with tomato sauce from last summer's tomatoes; also from the freezer are the green beans, Northeaster, a flat bean with rich flavor; the French Fingerling potato came from the root cellar.

2 cups chopped yellow onion
2 Tbs olive oil, butter, or a mixture
salt and pepper
1 cup lentils
1/2 cup finely diced celery
1/2 cup finely diced carrot
1 egg
2 cups soft bread crumbs, or 1 cup mashed potatoes and flour for dusting
vegetable oil for frying

1. Cook the onion in the olive oil in a medium skillet over low heat, covered, for 20 minutes. Remove the cover and cook, stirring from time to time, until the onions are brown and soft and smell delicious. Season with salt and pepper
2. Put the lentils, celery and carrot with 1 teas salt in a saucepan with water to cover by 3 inches. Bring to a boil, then simmer until lentils are tender, about 30 minutes. Drain, saving the liquid. When they have cooled a little, puree the lentils in a food processor, using some liquid if necessary, but leave a little texture. 
3. Mix lentils with the onion, half the bread crumbs or the cup of mashed potato; add the egg and mix well. Let cool until easy to handle, then form into rounds. I made 3 inch patties and got 10 from the recipe. Madison says you can get 18  2 1/2 inch patties. Place remaining bread crumbs or flour on a plate and dust the croquettes with it. Another tip from Jamie Oliver: put the croquettes in the refrigerator for an hour before cooking to help firm them up for frying. 
4. Fry croquettes in shallow oil until golden brown on both sides. 

I think this recipe makes enough for four for a main dish; Deborah Madison says six. I guess I'm a big eater.