Prepare the crust. Preheat the oven to 350°F and line a 8x8 metal baking pan with parchment paper, leaving at least 2 inches of overhang to help remove it from the pan later. If you haven't already, freeze the plant butter or coconut oil for just 5-10 minutes (any longer and the coconut oil will be hard as a rock and you'll need to let it sit out before mixing).

Add the almond flour, sweet rice flour, corn starch, sugar, and salt to a stand mixer fitted with the paddle attachment (or a food processor) and mix to combine Add the plant butter or coconut oil and vanilla. Mix or pulse, beginning on low and gradually increasing the speed to medium-high until the filling begins to clump together and the plant butter or coconut oil is fully incorporated. The dough should hold together when gently pinched with your fingers. This might take a few minutes - it will appear dry at first, but it will eventually clump into a coarse meal.

Dump the dough clumps into the bottom of the parchment-lined 8x8 baking pan. Press the dough evenly into the pan. Prick the bottom all over with a fork, and bake for 25-27 min until the crust is golden. Remove from the oven and while the crust is still hot, use a cup bottom or the back of a spoon to gently press down on the sides and bottom to help hold it together as it cools. Let cool for at least 20 minutes before adding the filling.

Prepare the filling. Whisk together the sugar and corn starch in a medium saucepan. Whisk in the lemon juice, coconut milk, and salt. Cook over medium heat, whisking until bubbling. Continue cooking for 3-4 more min until thickened to the consistency of runny yogurt.

Whisk in the turmeric, a little at a time, until completely combined and the desired vibrant color (it will brighten up as it cools). Remove from heat and whisk in the lemon zest.

Pour the filling into the cooled prepared tart crust and chill in the refrigerator for at least 2 hours until the filling is completely set before serving. After 2 hours, do a jiggle test to see if they're fully set or carefully tap the center with your finger. The filling should not stick to your finger when they're ready to slice.

To serve, gently lift the lemon bars out of the pan using the parchment paper. Use a sharp knife to release the lemon curd from the parchment paper. Wiping the knife between cuts, slice into 16 bars (4 x 4). Just before serving, dust generously with powdered sugar, if desired, or top with decorative lemon slices.

Store leftovers in an airtight container in the fridge.