1 (10 ounce) can crushed pineapple, drained
1/2 cup butter
1 (10 ounce) package frozen chopped spinach, thawed and drained
1 (8 ounce) package frozen whipped topping, thawed (optional)
Preheat oven to 350 degrees F (175 degrees C).
In a medium bowl, mix together the pineapple, butter and spinach. Spread over the bottom of a 9x13 inch baking dish.
Bake in preheated oven for 30 minutes. Remove from oven and let cool.
Spread the remaining chilled pineapple mixture over the top of the baked casserole. Top with whipped topping if desired.