Preheat Oven to 350°. Spread 2 tbsp of butter and 1/4 cup of plum jam on the flatbread and bake for 10 minutes. Be extremely careful when remove the flatbread (the jam is now somewhat caramelized and can burn) place on a cooling rack for 10 minutes.
Put lemon juice on plum and toss. Layer plum slices up and down the flatbread. Sprinkle brown sugar and chop up the rest of the butter and place on the top. Sprinkle cinnamon and place back in the oven for 15 minutes. Remove and cool for 10-15 before serving. Want to get fancy? Add a dollop of goat cheese for a little tang!