In the bowl of a food processor, combine the whole wheat flour, oats, salt and cinnamon.
Add in your cubes of cold butter and pulse until the butter is incorporated in pea sized bits.
Add in the sourdough starter, Greek yogurt, and maple syrup. Process until the ingredients come together and the dough begins to form a ball around the blade.
Place the dough in an airtight container or wrap it in plastic wrap and allow to rest for one hour. For fermentation benefits, place the dough in the refrigerator for 24 hours.
Prior to baking, preheat your oven to 350 degrees.
When ready to assemble, place the dough on a floured surface and use a rolling pin to roll the dough into a large rectangle. The dough should be 1/8 inch thick and form an 8×16 inch rectangle.
Use a knife to cut the dough into 4×4 inch squares.
Prepare an egg wash: Crack an egg into a small bowl and use a fork to quickly whisk the egg.
Using a pastry brush, egg wash all four sides of each square of dough. This will keep the seam sealed and prevent the jam from seeping out.
Place a tablespoon of jam in the center of each square of dough. To create a bar, take one edge of dough and fold it over the jam, pressing the edges to seal them. Repeat with the opposite side, enclosing the jam.
Place the bars seam side down and a baking sheet lined with parchment paper.
Bake for 20 minutes, or until the top is just turning golden. Remove and allow to cool completely on a wire rack.