Preheat oven to 400°F(200°C). Grease a 12-cup (3 L) baking dish; set aside.

In food processor, pulse DORITOS^® Nacho Cheese Flavored Tortilla Chips to make fine crumbs; set aside.

Peel and thinly slice potatoes (you should have 8 cups/2 L); transfer to a large bowl. Set aside.

Melt butter in a saucepan set over medium heat; whisk in flour. Cook for 2 to 3 minutes or until the mixture resembles a soft dough. Season with salt and pepper. Slowly whisk in 1 cup (250 mL) of milk at a time, whisking constantly, until all of the milk is incorporated. Cook, stirring, for 8 to 10 minutes or until the mixture is thick enough to coat the back of the spoon.

Reduce heat to simmer; stir in 2 cups (500 mL) of Monterey Jack cheese until melted. Remove from heat; stir in sour cream. Pour over potatoes; toss gently to coat. Fold in 1/4 cup (60 mL) bacon bits and 2 tbsp (30 mL) chives.

Transfer potatoes to the casserole dish, spreading evenly. Cover the dish with foil.

Bake for 60 to 70 minutes or until potatoes are tender. Remove foil; sprinkle remaining cheese, bacon, chives, and reserved DORITOS^® crumbs over top. Bake for about 15 minutes or until golden brown and bubbly. Let stand for 10 minutes.