Preheat your oven to 350 degrees Fahrenheit. Grease a 9 by 9 inch square baking pan with butter or line it with parchment paper, leaving an overhang on the sides to make it easy to lift the bars out later.
In a medium saucepan, combine the cranberries, granulated sugar, orange zest, and orange juice. Cook over medium heat for about 10 minutes, stirring occasionally, until the berries burst and the mixture thickens. Whisk the cornstarch with a teaspoon of water and stir it into the berries, then remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the all purpose flour, rolled oats, light brown sugar, baking powder, and salt. Ensure there are no large clumps of brown sugar so the texture remains consistent throughout the crust.
Add the cubed cold butter and the alcohol-free vanilla extract to the flour mixture. Use a pastry cutter or your clean fingertips to work the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea sized pieces of butter remaining.
Take about two thirds of the crumble mixture and press it firmly into the bottom of your prepared baking pan. Use the bottom of a measuring cup to pack it down into an even, solid layer that will support the fruit filling.
Spread the cooled cranberry filling evenly over the bottom crust. Sprinkle the remaining one third of the crumble mixture over the top, squeezing it slightly with your hands to create larger decorative clumps.
Place the pan in the center of the oven and bake for 35 to 40 minutes, or until the top is golden brown and the cranberry filling is bubbling at the edges. Remove from the oven and let the bars cool completely in the pan before slicing into squares.
