To start this recipe, go ahead and pull out your butter and eggs to allow them time to get to room temperature.
In a medium-sized pot, add cranberries, sugar, and water.
Heat to medium-high heat until simmering.
Continue to simmer until the cranberries break down. Use the back of a wooden spoon or spatula to crush the cranberries.
Once thickened and mostly smooth, remove from heat and allow to cool to at least room temperature.
Pre-heat the oven to 350º Fahrenheit.
In a medium sized mixing bowl, add softened butter, sugar, flour, lemon zest, and vanilla extract.
Use your hands (or an electric mixer) to combine the ingredients until crumbly but able to clump when squeezed together.
Line a 8x8 baking pan with a bit of butter or baking spray as well as parchment paper. Add the shortbread mixture to the pan and use your hands to press it down until it is roughly even and in all the corners.
Take a fork and lightly prick throughout the dough.
Bake at 350º F for 30 minutes.
Remove when done and allow to cool to room temperature.
Lower the oven to 325º F.
In a mixing bowl, combine 3 large eggs, lemon juice, and lemon zest.
In another bowl, whisk together flour and sugar. Add this to the bowl with the eggs and whisk together until smooth. The mixture will be quite thin.
Once the shortbread crust has cooled, add the cooled cranberry sauce to the top of the shortbread. Use a rubber spatula to spread evenly across the crust.
Grab a large spoon. Hold the bowl of lemon mixture in your dominant hand while holding the large spoon in your other hand. Hold the spoon upside down over the cranberry layer (so that the curved/rounded part is facing up).
Very slowly, pour the lemon mixture onto the spoon over the cranberry mixture. The lemon mix will hit the spoon first before falling onto the cranberry. This helps the layers stay even and not mix.
Once poured, carefully transfer to the oven and bake at 325º F 25-35 minutes. It is done when the center of the pan no longer jiggles.
Remove and cool in the refrigerator for at least 2 hours or overnight.
Sprinkle with powdered sugar, slice, and serve.