Preheat your oven to 350 degrees Fahrenheit. Line a 9×9 inch baking pan with parchment paper, leaving a bit of an overhang on the sides to make it easy to lift the bars out later.
In a large mixing bowl, combine the flour, rolled oats, brown sugar, salt, and baking soda. Use a pastry cutter or your clean fingertips to work the cubed butter into the dry ingredients until the mixture resembles coarse crumbs. Press about two-thirds of this mixture firmly into the bottom of your prepared pan to form the base crust.
In a medium bowl, toss the fresh cranberries with the granulated sugar, cornstarch, orange juice, and alcohol-free vanilla extract. Stir until the berries are evenly coated. The cornstarch will help thicken the juices as the fruit bakes, ensuring the bars do not get soggy.
Spread the cranberry mixture evenly over the bottom crust. Sprinkle the remaining one-third of the oat mixture over the top of the berries, pressing down very lightly to help it stick. Bake for 40 to 45 minutes, or until the topping is golden brown and the cranberry filling is bubbling around the edges.
Remove the pan from the oven and let it cool completely on a wire rack. This step is crucial because the bars need time to set before you slice them into squares.
