Preheat oven to 375 degrees Fahrenheit.

Bake potatoes for 1 hour or until fork tender.

Let potatoes cool until they are cool enough to handle.

Split potatoes in half and remove the potato pulp, leaving a 1/4 inch thick shell.

In a large bowl, mix together potato pulp, butter, salt, pepper, spinach, and cheese.

Grease a 2 quart baking dish.

Place empty potato shells into the baking dish.

Divide the potato/spinach mixture evenly into the potato shells.

Bake for another 20 to 25 minutes or until cheese is melted and tops are lightly browned.

Let cool before serving.