1 jar (12 ounces) pickled jalapeno pepper slices, drained (optional)
2 cups (8 ounces) shredded cheddar cheese
2 cups (8 ounces) shredded Monterey Jack cheese
2 cups (16 ounces) sour cream (for topping)
6 to 8 green onions, chopped (optional)
Place potatoes in a saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 15-20 minutes or just until tender. Drain; cool slightly.
Cut potatoes into 1/4-in.-thick slices. Place in a single layer in three greased 15-in. x 10-in. x 1-in. baking pans. Top each with salad dressing mix, a jalapeno slice, cheddar cheese and Monterey Jack cheese.
Bake, uncovered, at 350° for 10-12 minutes or until cheese is melted. Top with sour cream and green onions.