Combine sugar and lemon juice in a saucepan over medium heat and simmer until sugar is dissolved. Add peaches, plums, nutmeg, and pumpkin pie spice and cook for five to seven minutes, until soft, stirring every few minutes. Dissolve cornstarch and water and add to the pot. Simmer for another five minutes until thickened and set aside. This can be done in advance and kept in the refrigerator for up to a week.

Microwave stroopwafels for 10 to 15 seconds, until softened enough to be pliable. Gently bend into a taco shape. Flip over a muffin pan and stand the waffle in the crevice. Let sit to harden.

Warm fruit filling and fill waffles immediately before serving.