Preheat oven to 350 degrees. In large pot coated with nonstick cooking spray, saut the onion over a medium high heat for 5 minutes. Add fresh* sweet potatoes and 2/3 cup chicken broth. Bring mixture to a boil and simmer over medium heat for 10 to 15 minutes or until sweet potatoes are tender. If using canned yams, add them and 2/3 cup chicken broth to sauted onion; heat thoroughly. Add flour, stirring. Gradually add milk, stirring until well combined. Add ham. Bring to a boil and transfer mixture to a 7x11 inch baking dish coated with nonstick cooking spray. If mixture is too thick, add more broth or milk. Unfold crust to round circle; sprinkle pecans on one side. Fold in half and roll with rolling pin, pressing pecans into crust. Spread pecan crust on top of mixture and bake for 30 minutes or until crust is brown; sprinkle with thyme.