Butter 13x9x2-inch baking dish. Cook baconin heavy large skillet until golden brownand crisp.
Transfer to paper towels to drain.Chop bacon.
Place in medium bowl.
Addgreen onions; toss to distribute evenly.
Place potatoes in large pot and addenough cold water to cover.
Sprinkle withsalt. Cover and boil with lid slightly ajaruntil potatoes are tender, 15 to 20 minutes.
Drain well.
Return potatoes to pot. Cook overlow heat, stirring often, until potatoes aredry and light film forms on bottom of pot,about 2 minutes.
Add next 3 ingredients.Using potato masher, mash until almostsmooth. Stir in 1 1/2 cups smoked Gouda and1 cup bacon mixture. Season with salt andpepper.
Spread potato mixture in preparedbaking dish.
Sprinkle remaining 1/2 cup
Gouda over. DO AHEAD: Can be prepared 8hours ahead. Cover and chill potato mixtureand remaining bacon mixture separately.
Preheat oven to 375°F.
Bake potatoesuntil cheese melts and edges of potatoesare bubbling, about 30 minutes (40 minutesif chilled).