In a dutch oven or stock pot melt 1 tablespoon of butter and saute the onions, celery and carrots for a few minutes. Add ham and potatoes and continue sauteing
Add about 1 1/2 cups of milk to the ham and veggies, some thyme and a bay leaf. Simmer this mixture while you prepare the cream base for the soup and allow the potatoes to cook through.
In a medium saucepan melt 6 tablespoons of butter and add the flour stirring to make a roux, allow to cook on low stirring constantly for 3-4 minute. be careful not to burn it.
Add all the milk at once, while whisking constantly. allow to simmer until it reaches the thickness that you are wanting for your chowder.
Add the roux to your ham and veggies, at this time I would add both of the squash. I personally do not like over done squash so simmer just until they are aldente. Adjust the seasoning and enjoy!