Heat EVOO in a large soup pot over medium-high heat. Add fennel, squash, carrots, parsnips, onions, leeks, garlic, fresh and dried herbs. Cook partially covered, stirring occasionally to soften, 8-10 minutes. Add stock and simmer while you make white sauce.
In a saucepan, melt butter over medium heat. Whisk in flour, cook 1-2 minutes then add milk and simmer to thicken. Season with salt, pepper and nutmeg. Once thickened, combine sauce with soup and keep warm over low heat until ready to serve. Top each bowl with oyster crackers.