1. Preheat the oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on two sides, and lightly grease any exposed parts of the pan.

2. Make the crust: In a medium bowl whisk together the 2 cups flour, 1/2 cup powdered sugar, and 1/4 teaspoon salt. Stir in the melted butter until the mixture looks like soft, moist sand.

3. Press the crust mixture firmly and evenly into the bottom of the prepared pan, pressing it into the corners. Bake for 15–18 minutes, until the edges are lightly golden and the surface looks set but not deeply browned.

4. While the crust bakes, make the lemon filling: In a large bowl whisk together 1 1/2 cups granulated sugar and 1/4 cup flour. Add the eggs, 2/3 cup lemon juice, lemon zest, vanilla, and a pinch of salt. Whisk until smooth and slightly frothy.

5. When the hot crust comes out of the oven, immediately pour the lemon filling over the top, tilting the pan gently so it spreads into an even layer.

6. Return the pan to the oven and bake for 18–20 minutes, until the center is just set with a very slight jiggle when you nudge the pan. Transfer to a cooling rack and let the lemon layer cool for about 10 minutes.

7. While the lemon layer bakes and cools, make the cranberry topping: In a medium saucepan combine the cranberries, 3/4 cup sugar, water, and 1 tablespoon lemon juice. Bring to a gentle simmer over medium heat.

8. Cook the cranberries, stirring occasionally, for 8–10 minutes, until most of the berries have burst and the mixture looks thick and glossy.

9. Stir the cornstarch into a teaspoon or two of cool water to make a slurry, then stir it into the cranberry mixture. Let it bubble for 1 minute more, until nicely jammy. Remove from heat and cool for 10–15 minutes until warm but not piping hot.

10. Gently spoon the cranberry topping over the warm lemon layer, spreading it to the edges without pressing down too hard. Let the bars cool completely at room temperature, then refrigerate for at least 2 hours or until thoroughly chilled.

11. Use the parchment overhang to lift the chilled bars out of the pan onto a cutting board. Dust generously with powdered sugar, then cut into 16 squares (or smaller bars if you prefer). Serve chilled or just slightly cool.