Preheat oven to 180. Cut squash in 1/2 and brush with olive oil.
Bake until tender - 45 min.
Saute leeks in butter for 10 min. Add squash, stock, and seasonings.
Bring to boil and simmer 10 min.
Puree soup.
Return to heat bring to boil,reduce heat and Add buttermilk, but do not let soup boil