Lentil-sausage soup

This is an incredibly warming, filling winter soup. To be honest, I don't really adore lentils, but I like them a lot more if they're well seasoned. I find that starting with a mirepoix and adding the balsamic vinegar and cilantro at the end give the soup an interesting flavor that makes the lentils bearable. Which is great, because they're so relentlessly healthy--superbly high in fiber, protein, and all sorts of vitamins and minerals. And absurdly cheap, too. The sausage is optional--I just put it in because Baby B loves sausage above almost any other food.

Ingredients:
1 1/2 cups brown lentils
5 cups homemade chicken broth (if you buy broth, get the low-sodium kind)
5 cups water
2 tablespoons olive oil
2 onions, finely chopped
3 stalks of celery, finely chopped
1 medium carrot, finely diced (I don't bother peeling it, but feel free if you prefer)
3 cloves of garlic, crushed with the blade of a knife, peeled, and minced
1 teaspoon dried oregano
1 teaspoon ground cumin
1/4 cup cilantro, minced
1/8 cup balsamic vinegar, or more to taste
kosher salt and freshly ground pepper
1/2 pound mild or spicy Italian sausage (pork, turkey, chicken, or vegetarian sausage would all work well)

Place the lentils in a large bowl and cover with boiling water for an hour to soften the lentils. Drain.

Now boil the lentils in the water and broth for about 25 minutes, or until the lentils are cooked.

While the lentils are boiling, heat the oil in a cast-iron frying pan (or non-stick) over medium-high heat. Add the onions, celery, carrot, a pinch of kosher salt, and a grinding of pepper, and cook, stirring frequently, for about 15 minutes. Add the garlic, oregano, and cumin, and cook a further minute or two, stirring constantly.

When the lentils are almost cooked, add the vegetables and simmer for another 10-15 minutes while you cook the sausage. In the same pan as before, saute the sausage, breaking it up with a wooden spoon to crumble it. Cook until there are no pink bits remaining.

Add the sausage to the lentils. Stir in the balsamic vinegar and the cilantro. Adjust the seasonings to taste.

Serve with toast or grilled cheese sandwiches.