COVER potatoes and garlic with water in large saucepan. Bring to boil on high heat. Reduce heat to low; simmer 20 min. or until potatoes are very tender. Drain; return to saucepan with sour cream. Mash to desired consistency. Stir in 1/4 cup of the Cheddar cheese.
PREHEAT oven to 375°F. Brown meat in large nonstick skillet. Stir in flour; cook 1 min. Add vegetables, broth and ketchup; continue cooking 5 min.
SPOON meat mixture into 8-inch square baking dish. Cover with mashed potatoes. Bake 18 min.; sprinkle with remaining 1/4 cup Cheddar cheese. Bake an additional 2 min. or until heated through and cheese is melted.