Heat a large Dutch oven over medium high heat and melt the butter. Add onion to the hot butter and cook until translucent. Stir in the garlic and ham and cook for 2-3 minutes. Add in the thyme, sage, salt and pepper, broth and bay leaf. Stir in the potatoes, bring to a boil and cook until potatoes are tender, about 15 minutes. Whisk in the cornstarch slurry, corn and broccoli and coo until soup begins to thicken. Turn heat to LOW and whisk in the half and half, sour cream and cheese. Heat until just steaming (do not boil) and serve immediately.