Spinach Twice-Baked Potatoes

4 large baking potatoes, scrubbed well
1 package frozen chopped spinach, thawed OR 2 cups chopped fresh spinach
¼ cup butter
¼ cup sour cream
½ cup warm milk, approximately
2 cups grated cheddar cheese
salt and pepper
1 pinch cayenne

Cut a small slit on top of each potato, and place in a 400 degree oven for 1 hour or until baked through.
Cut each potato in half, lengthwise, and scoop flesh into large bowl.
Place the potato shells on a baking sheet.
If using frozen, squeeze the spinach to drain the water; it needs to be fairly dry.
If using fresh, chop the spinach.
Set aside.
Mash the potatoes in the bowl with the butter, sour cream and milk, salt, pepper and cayenne. (I leave mine a little chunky, as Hubs prefers smashed to mashed.)
Fold in the spinach and 1/2 the cheddar cheese.
Fill potato shells with this mixture.
Top with remaining cheddar cheese.
These potatoes can be made in advance and kept in the refrigerator for a day prior to baking.
Bake at 350 for about 30 minutes or until heated through and the cheese on top has melted and browned a little. (Serves 6-8)