Preheat oven to 500°.
Pierce the potatoes with a fork, and arrange in a circle on paper towels in microwave oven. Cover potatoes with damp paper towels. Microwave potatoes at high 12 minutes or until done, rearranging after 6 minutes. Let stand 2 minutes. Split open potatoes; scoop out pulp, leaving a 1/4-inch-thick shell. Reserve shells; set pulp aside.
Heat butter in a small skillet over medium-high heat. Add garlic; sauté 30 seconds. Add milk; bring to a simmer. Pour milk mixture over potato pulp. Add 1/4 cup cheese, ham, and remaining ingredients, mixing well. Stuff shells with potato mixture. Sprinkle evenly with 1/4 cup cheese. Bake at 500° for 8 minutes or until the cheese begins to brown.