Begin by rinsing 8 ounces of fresh cranberries under cool water. In a saucepan, combine the cranberries with 1/2 cup of water and 6 tablespoons of sugar. Cook over medium heat for about 10-15 minutes, stirring occasionally, until the cranberries burst and soften into a thick sauce. Allow the mixture to cool for 30 minutes before using.

Preheat your oven to 325°F (160°C). Line a 9-inch square baking dish with parchment paper for easy removal. In a mixing bowl, blend 1/2 cup of melted unsalted butter, 1/4 cup of sugar, 1 teaspoon of vanilla extract, and 1/4 teaspoon of salt. Gradually add 1 cup plus 1 tablespoon of all-purpose flour, mixing until a soft dough forms. Press this dough evenly into the prepared pan and bake for 16-18 minutes.

In a medium bowl, whisk together 3 tablespoons of flour and 1 cup of sugar until blended. Add 3 large eggs and 1/2 cup of freshly squeezed lemon juice. Whisk until smooth.

Once the cranberry mixture has cooled, pour it evenly over the baked shortbread crust. Cover and refrigerate for about 45 minutes.

Preheat your oven to 350°F (175°C). Pour the lemon mixture over the chilled cranberry layer and bake for 43-45 minutes. Remove from oven and let cool for 1 hour.

Place the pan in the refrigerator for an additional 1-2 hours to firm up the layers. Dust with powdered sugar just before serving.