Core cabbage and pull apart leaves. Blanch in large pot of boiling salted water until pliable, 2 to 4 minutes. Chill under cold water; drain.

Separate and peel garlic cloves. Place in saucepan with potatoes and half of the onion; cover with water. Bring to boil; reduce heat to simmer. Cook until potatoes are tender, 15 to 20 minutes; drain. Return to saucepan over low heat; heat until excess moisture has evaporated, 1 minute. Mash well; stir in 1/2 tsp (2 mL) each salt and pepper and 1-3/4 cups (425 mL) of the cheese.

Meanwhile, in skillet over medium-high heat, heat 2 tbsp (30 mL) oil; add remaining onion and sauté until golden, 12 minutes. Stir in tomatoes and pinch each salt and pepper. Set aside.

Reserve 12 large cabbage leaves; cut out hard centre rib. Coarsely chop remaining leaves; place in bottom of greased 13- x 9-inch (3 L) baking dish. Place 1/3 cup (75 mL) potato mixture on a reserved cabbage leaf; roll, folding in sides, to form packet. Repeat with remaining leaves; place in casserole. Scrape onion mixture over rolls; sprinkle with remaining cheese. Cover with greased foil. Bake in 375F (190C) oven until cabbage is tender, 1 hour. Uncover; bake until most of the liquid has evaporated and top is lightly browned, 10 to 15 minutes.

Makes 6 servings.