Preheat the oven to 350 F and line an 8 x 8-inch square pan with parchment paper on all sides. Set aside.
First, make the filling. Pit the peaches and slice them into ¼ inch thick slices. Place a heavy bottomed saucepan over medium heat and combine ⅔ of the sliced peaches with the brown sugar, flour, and cinnamon (if using). Stir with a rubber spatula and cook for 10 minutes or until the peaches have fully broken down and formed a thick jam. Add the uncooked peaches and stir to combine. Set aside.
Next, make the crumb dough. In a stand mixer fitted with the paddle attachment, combine the softened butter, Domino® Light Brown, vanilla, flour, salt, and baking powder. Mix on low speed until the mixture starts to clump together and form a thick dough, about 3 minutes, scraping down the sides of the bowl as needed. It will seem crumbly at first and like it won’t come together but it will!
Press about ⅔ of the mixture into the prepared pan, using your fingers or the bottom of a measuring cup to pat it into an even layer. Spread the peach jam over the bottom crust all the way to the edges. Sprinkle the remaining topping in small and big clusters all over the peaches.
Bake until the peaches are bubbling and the top of the bars is golden brown, 35 to 40 minutes.Place the pan on a cooling rack and allow the bars to cool completely before slicing and serving!