Cook potatoes in boiling water in large saucepan 20 min. or until tender; drain. Return to pan.
Heat oven to 350 degrees F. Add margarine and sour cream to potatoes; mash until smooth. Spoon half into 1.5-L casserole dish; cover with layers of cheese, remaining potato mixture and bacon.
Bake 30 to 35 min. or until heated through.
Do not beat the potatoes in a nonstick pan as this could damage the nonstick surface. Transfer potatoes to a large bowl, then beat potatoes as directed.
How to Make Potatoes Creamier: Add 2 Tbsp. milk to the drained cooked potatoes along with the margarine and sour cream.
Know How: Avoid using an electric mixer for mashing potatoes. The biggest drawback with electric mixers is that they can over work the potatoes to the point that the starch breaks down. It will result in mashed potatoes that are sticky and have a gummy consistency.
Special Extra: Add 1 tsp. minced garlic to drained cooked potatoes along with the margarine and sour cream.