Ingredients
1 tb margarine, dairy free
1 tb Vegetables oil
1 c onion – chopped
8 oz Mushrooms – sliced
1 lg Garlic clove – minced
1/3 celery – thinly sliced
3 c Soybean milk
4 c Potatoes – cubed ½ inch
¼ ts Black pepper
1 ts Salt, or to taste
1 tb Parsley – chopped

Directions
1. Saute onion, garlic, celery, and green pepper in hot oil and margarine about 3 minutes. Add sliced mushrooms and sauté 3 more minutes.
2. Add soybean milk, black pepper, salt and potatoes. Bring mixture almost to a boil; reduce heat and simmer 25 minutes, stirring occasionally.
3. Make about 6 cups. Thin with extra soybean milk if soup is too thick.
4. Garnish with parsley and serve with the veal.

According to the text when should we add sliced mushroom?