OK, this is NOT how I make roasted vegetable soup. I don't get throwing them out, for starters, and I don't want to spend all that time. So, I'd just go as far as the making the stock stage, stop when it tastes good, and, you know me, add some nice sausage (patties, leftover chicken bits, whatever), maybe some sliced mushrooms, and some broken up pasta and cook until the pasta is done.
but here's a how to do it the right way recipe from the LA Times...
http://www.latimes.com/features/food/la-fo-encore031408-rec1,1,454354,full.story
Recipe: Roasted vegetable soup
Total time: 2 hours, 50 minutes
Servings: 4 to 6 servings
Roasted vegetable stock
2 cups diced onion
2 carrots, scrubbed and diced (about 1 cup)
3 stalks celery, diced (about 1 cup)
6 whole peeled cloves garlic
2 cups peeled, diced celery root
3 tablespoons olive oil
1/2 teaspoon salt
1/4 teaspoon pepper
2 leeks, white part only
10 peppercorns
1 bay leaf
3 to 4 sprigs thyme
3 to 4 sprigs parsley
1/2 cup dried porcini mushrooms
2 Yukon Gold potatoes
1. Heat the oven to 425 degrees. Toss together the onion, carrots, celery, garlic and celery root with the olive oil, salt and pepper in a large baking pan. Roast 35 to 45 minutes or until vegetables are lightly browned, stirring occasionally.
2. Place the roasted vegetables in a tall 8-quart stockpot. Cut the leeks into quarter-inch slices and add them to the pot. Add the peppercorns, bay leaf, thyme, parsley and dried mushrooms. Peel the potatoes and add the peels to the pot. Cut the peeled potatoes into half-inch dice, cover them with cold water, and set aside to use in the soup. Add 10 cups cold water to the stockpot.
3. Bring the mixture to a boil over high heat. Reduce the heat to a simmer and cover. Simmer 45 minutes.
4. Remove the pot from the heat. Strain the stock through a cheesecloth-lined strainer, lightly pressing the vegetables with the back of a spoon to extract juices. Discard the vegetables. You will have about 8 cups of stock.
Soup
2 cups sliced cremini mushrooms
4 teaspoons plus 2 tablespoons olive oil, divided
Kosher salt
White pepper
1 medium onion, diced (about 1 cup)
1/2 cup diced celery
1/2 cup diced carrot
2 cloves garlic, minced
1/2 cup dried small white beans
8 cups roasted vegetable stock
3 cups coarsely chopped savoy cabbage
Yukon Gold potatoes, reserved from stock recipe
1/4 pound each green beans and yellow beans, stems removed, cut diagonally into 1-inch pieces
Sliced, toasted French bread
1. Heat the oven to 425 degrees. Toss the sliced mushrooms in a bowl with 4 teaspoons olive oil, one-eighth teaspoon salt and a pinch of white pepper. Place in a baking pan and roast for about 13 minutes, until tender and lightly browned. Remove from the oven and let stand.
2. Saute the onion, celery and carrot in 2 tablespoons olive oil in a tall 8-quart stockpot until tender, about 5 minutes. Add the garlic and saute 1 minute.
3. Add the white beans, vegetable stock, cabbage and 1 teaspoon salt. Bring the mixture to a boil over high heat, then reduce heat to a simmer, cover and cook about 1 hour, stirring occasionally.
4. Add the drained potatoes and the mushrooms during the last 30 minutes of cooking.
5. Add the green and yellow beans during the last 15 minutes of cooking and simmer until the beans are crisp-tender. Season to taste with salt. Serve the soup with toasted French bread brushed with good olive oil.
Each of 6 servings: 271 calories; 8 grams protein; 30 grams carbohydrates; 10 grams fiber; 15 grams fat; 2 grams saturated fat; 0 cholesterol; 451 mg. sodium.