Cook persimmons and strain. May use food mill for straining. If using a blender, the seeds must be removed first. Measure the pulp and add equal amount of sugar. Put into heavy kettle; stir in 1/2 teaspoon baking soda to each cup of pulp. Flavor with pumpkin pie spice , grated lemon, or grated orange rind and juice. Cook until it is medium thick, like apple butter. The soda will cause it to foam, but later this disappears and the butter turns a deep dark red.