Mashed-Potato Casserole with Gouda and Bacon

Butter 13x9x2-inch baking dish. Cook bacon in heavy large skillet until golden brown and crisp. Transfer to paper towels to drain. Chop bacon. Place in medium bowl. Add green onions; toss to distribute evenly. Place potatoes in large pot and add enough cold water to cover. Sprinkle with salt. Cover and boil with lid slightly ajar until potatoes are tender, 15 to 20 minutes. Drain well. Return potatoes to pot. Cook over low heat, stirring often, until potatoes are dry and light film forms on bottom of pot, about 2 minutes. Add next 3 ingredients. Using potato masher, mash until almost smooth. Stir in 1 1/2 cups smoked Gouda and 1 cup bacon mixture. Season with salt and pepper. Spread potato mixture in prepared baking dish. Sprinkle remaining 1/2 cup Gouda over. DO AHEAD: Can be prepared 8 hours ahead. Cover and chill potato mixture and remaining bacon mixture separately. Preheat oven to 375°F. Bake potatoes until cheese melts and edges of potatoes are bubbling, about 30 minutes (40 minutes if chilled). Sprinkle reserved bacon mixture over and serve.