Preheat the oven to 350 F (177 C). Line an 9 x 9 (23 cm) aluminum pan with parchment paper along the bottom and two sides.
Add the fresh or frozen cranberries, sugar, orange zest and cornstarch to a large mixing bowl. Toss the ingredients together until the cranberries are fully coated. Set aside while making the shortbread crust and crumble topping.
3 cups fresh or frozen cranberries, ½ cup (100 g) granulated sugar, 1 tablespoon cornstarch, 1 tablespoon orange zest
Make the buttery crust and crumb topping by combining the flour, sugar, baking powder, cinnamon and salt together in a food processor. Pulse 2 -3 times to combine the ingredients. Pulse in cubes of cold butter until the mixture resembles a crumble texture. Finally pulse in the egg yolk and vanilla extract until the mixture starts to clump together.
2¼ cups (270 g) all purpose flour, ¾ cup (150 g) granulated sugar, 1 teaspoon ground cinnamon , ½ teaspoon baking powder, ½ teaspoon salt, ¾ cup (170 g) cold unsalted butter, cubed, 1 large egg yolk, 1 teaspoon vanilla extract
Evenly press ? of the shortbread mixture into the prepared pan. Transfer the cranberry filling onto the shortbread crust. Top the cranberry filling with the remaining ⅓ crumble mixture. Make sure to cover as much of the filling as much as possible, but spots of exposed filling is fine.
Bake the cranberry bars for 45 - 55 minutes or until the crust is a nice golden brown with edges of the crust pulling slightly away from the sides of the pan. The cranberry filling will thicken and bubble.
Cool the cranberry crumble bars in the pan for 1 hour. If the bars are too soft to easily transfer from the pan after 1 hour at room temperature, transfer to the fridge to set for another hour. Once the bars are set, top with powdered sugar or orange vanilla maple glaze or enjoy as is.