1/4 cup (1/2 stick) unsalted butter

5 Leeks white and pale green parts only --

chopped(about 3c) 1 Onion--chopped

10 ounces Portobella mushrooms -- chopped (about 4

-- generous cups) 1/4 cup All-purpose flour

3 cups Chicken stock or canned low-salt broth

4 tablespoons Dry Sherry

2 cups Half and half

1/4 teaspoon Cayenne pepper

Ground white pepper

Melt butter in heavy large Dutch oven over medium heat. Add leeks and onion; sa ut_