In a saucepan over medium heat, combine the fresh cranberries, granulated sugar, and water. Cook, stirring occasionally, until all of the cranberries have popped and the mixture is thick, which should take about 15 minutes. Once thickened, remove the pan from the heat and set aside to cool before using. I find cooking the cranberries until they fully burst brings out their natural tartness and gives a jammy texture that's perfect for bars.

In a separate bowl, sift together the all-purpose flour and kosher salt, then set aside. In a large mixing bowl, beat the softened unsalted butter until smooth. Add the light brown sugar and vanilla extract, and continue beating on medium-low speed until the mixture is creamy and smooth. Gradually add in the flour mixture and beat just until incorporated—the dough should form clumps but not come together as a solid ball.

Preheat the oven to 350°F (175°C). Lightly oil an 8x8 inch square pan. Press about two-thirds of the shortbread dough (from Step 2) evenly into the bottom of the prepared pan. Lightly prick the surface with the tines of a fork. Bake the shortbread base for 17 to 18 minutes, or until it is lightly browned. Once baked, remove the pan from the oven and set aside. For a softer base, don't overbake at this stage—you want the bars to hold together but still have some tenderness.

Evenly spread the cooled cranberry filling (from Step 1) over the baked shortbread base, leaving a 1/4-inch border around the edges. Using your fingers, crumble the remaining third of the shortbread dough (from Step 2) over the top of the cranberry layer. Lightly press the crumbled dough into the cranberry filling to help it adhere.

Return the pan to the oven and bake for 25 to 30 minutes, or until the top is golden brown. Remove the pan from the oven and place it on a wire rack. While still warm, use a sharp knife to cut the bars into 16 squares. Allow the bars to cool completely in the pan before serving. I like to let these bars cool overnight—the flavors meld beautifully, and they cut even more cleanly the next day.