Phase 1: Preparing the Perfect Vegan Shortbread Crust

1. Preheat and Prep: Preheat your oven to 350°F (175°C). Line an 8×8 inch (20×20 cm) square baking pan with parchment paper, leaving an overhang on two opposite sides. This “sling” will make it easy to lift the squares out later. Lightly grease the pan before adding the parchment if you want extra non-stick security.
2. Combine Dry Ingredients: In a medium-sized mixing bowl, whisk together the 1 ½ cups of all-purpose flour, ½ cup of granulated sugar, 2 tablespoons of cornstarch, and ¼ teaspoon of salt. If using, add the 1 teaspoon of lemon zest and whisk again to distribute.
3. Cut in the Butter: Add the ¾ cup of cold, cubed vegan block butter to the dry ingredients. Using a pastry blender, your fingertips, or a food processor (pulse carefully), cut the butter into the flour mixture until it resembles coarse crumbs or wet sand. Don’t overmix; some small pea-sized butter pieces are fine.
4. Press into Pan: Transfer the crumbly mixture to your prepared baking pan. Press it down firmly and evenly across the bottom of the pan using your fingers or the flat bottom of a glass. Aim for a compact, level base.
5. Pre-Bake the Crust: Bake the crust in the preheated oven for 15-18 minutes, or until it’s lightly golden around the edges and set. Pre-baking ensures a crisp crust that won’t get soggy under the lemon filling.
6. Cool Slightly: Once baked, remove the crust from the oven and set it aside to cool slightly while you prepare the lemon filling. Keep the oven on.

Phase 2: Whisking Up the Vibrant Vegan Lemon Filling

1. Combine Dry Filling Ingredients: In a large mixing bowl, whisk together the 1 ¼ cups of granulated sugar, ½ cup of cornstarch, 2 tablespoons of all-purpose flour, ¼ teaspoon of turmeric powder (if using for color), and ¼ teaspoon of salt. Whisking these dry ingredients thoroughly helps prevent lumps when the wet ingredients are added.
2. Add Wet Ingredients: Pour in the 1 can (400ml) of well-shaken full-fat coconut milk, ¾ cup of fresh lemon juice, and the 2 tablespoons of lemon zest.
3. Whisk Until Smooth: Whisk everything together vigorously until the mixture is completely smooth and no lumps of cornstarch or flour remain. This might take a minute or two. Ensure you scrape the bottom and sides of the bowl to incorporate everything. The mixture will be quite liquid at this stage.

Phase 3: Assembling, Baking, and Chilling to Perfection

1. Pour Filling Over Crust: Gently pour the prepared lemon filling mixture over the slightly cooled, pre-baked shortbread crust in the baking pan.
2. Bake the Squares: Carefully transfer the pan back into the 350°F (175°C) oven. Bake for 25-30 minutes. The filling should look set around the edges and still have a slight wobble in the very center (like a cheesecake). The surface might have a few tiny bubbles. Be careful not to overbake, as this can make the filling rubbery.
3. Cool Completely at Room Temperature: Once baked, remove the pan from the oven and place it on a wire rack. Let the lemon squares cool completely at room temperature. This can take 1-2 hours. Do not attempt to cut them or chill them while hot, as the filling needs to continue setting.
4. Chill Thoroughly: Once cooled to room temperature, cover the pan loosely with plastic wrap (try not to let it touch the surface of the filling) and transfer it to the refrigerator. Chill for at least 4 hours, but preferably overnight. This chilling process is crucial for the filling to firm up properly, allowing for clean, neat slices.
5. Slice and Serve: Once thoroughly chilled, use the parchment paper overhangs to carefully lift the entire slab of lemon squares out of the pan and onto a cutting board. Using a large, sharp knife, cut into squares. For the cleanest cuts, wipe the knife clean with a damp cloth between each slice. A classic dusting of powdered sugar before serving is highly recommended!