Fill a drinking glass or pitcher with the lemonade. Add the pumpkin puree, one tablespoon at a time, to taste (for a typical 8-ounce drinking glass, I like about 2 tablespoons of puree). Be sure to gently stir the lemonade after each addition so the puree becomes fully incorporated into the drink. Garnish with cinnamon or nutmeg to taste. Serve cold.