Cheddar Spinach Twice-Baked Potatoes

6 large baking potatoes (about 12 ounces each)
1/2 cup 2% milk
6 tablespoons butter, softened
1 package (10 ounces) frozen chopped spinach, thawed and squeezed dry
3/4 cup shredded Monterey Jack cheese
3/4 cup shredded cheddar cheese, divided
1/4 cup finely chopped red onion
1 teaspoon salt
1/4 teaspoon pepper

Preheat oven to 375°. Scrub potatoes; pierce several times with a fork. Place in a foil-lined 15x10x1-in. baking pan; bake 60-70 minutes or until tender.

When cool enough to handle, cut each potato lengthwise in half. Scoop out pulp, leaving 1/4-in.-thick shells. In a large bowl, mash pulp with milk and butter, adding spinach, Monterey Jack cheese, 1/4 cup cheddar cheese, onion, salt and pepper.

Spoon into potato shells; return to baking pan. Sprinkle with remaining cheddar cheese. Bake 20-25 minutes or until heated through and cheese is melted. Makes 12 servings.