Preheat oven to 375°F. Lightly spray a 9 X 13-inch baking pan.
In a food processor, pulse whole wheat flour, buckwheat flour, coconut sugar, salt, and baking powder in a food processor until well combined. Add butter cubes and pulse until the mixture is crumbly. Add egg, honey, and molasses and pulse until well combined and large clumps form. Reserve 1/2 cup of the mixture and pour the remainder into a prepared baking pan and press into the bottom and slightly up the sides to form a crust.
Bake for 10 minutes, remove from oven and cool.
For the Filling
Combine all ingredients in a food processor and lightly pulse together just to combine ingredients. Pour into a small saucepan and heat on medium heat until preserves had melted and a sauce begins to form. Pour over cooled crust and crumble reserved 1/2 cup of crust mixture on top.
Bake for about 20 minutes until filling is bubbly and top begins to lightly brown. Cool completely before cutting and serving. If desired, sprinkle with powdered sugar.