Special equipment: a pastry bag fitted with a large round tip
Preheat the oven to 375 degrees F. Spray a 6-cup standard muffin tin (or the 6 middle cups of a 12-cup tin) with cooking spray and set aside. Whisk together the heavy cream and eggs in a large bowl and sprinkle with some salt and pepper. Add the leftover creamed spinach and thoroughly combine. Divide the spinach mixture among the muffin cups in the prepared pan. Bake in the middle of the oven until the tops are golden and they spring back to the touch, about 25 minutes. Allow to cool to just warm or room temperature before frosting.
Meanwhile, add the feta and cream cheese to the bowl of a food processor and pulse until light and fluffy. Transfer to a pastry bag fitted with a large round tip.
Pipe the tops of each of the spinach cupcakes with some of the feta frosting. Top each with a sprinkle of paprika and some chopped chives and serve.