Preheat the oven to 350°F. Lightly oil a 9 x 9 inch square baking pan, or line it with parchment paper that hangs over two sides so you can lift the bars out later.

Make the base by stirring together the flour, sugar and salt in a medium mixing bowl. Add the coconut oil and cut it in using a pastry cutter or a fork, until the mixture resembles fine crumbs. Stir in the milk to form a dough, continuing to stir or mix with your hands until it's nice and uniform.

Press the dough evenly into the bottom of the prepared baking pan. Place it into the oven and bake just until the edges begin to brown, about 20 minutes.

While the base bakes, make the curd. Place the lemon juice, sugar, cornstarch, lemon zest, lemon extract, salt, and turmeric (if using) into a small saucepan. Whisk until uniformly combined. Place the saucepan over medium heat and whisk in the coconut cream. Continue to whisk the mixture constantly as it heats up. The mixture should thicken up quickly once it gets to a simmer. Cook about 1 minute more, continuing to whisk vigorously, then remove the saucepan from the heat.

Once the base comes out of the oven, pour the lemon mixture over it, and smooth it out into an even layer. Return the pan to the oven and bake about 15 minutes longer. You should see a few bubbles forming in the curd by this time.

Remove the pan from the oven and transfer it to a cooling rack. The curd will continue to set as it cools. Let it cool completely, about 2 hours, then refrigerate for at least 1 hour so the curd firms up. Slice into 16 bars, wiping the knife clean between cuts.

Sprinkle with powdered sugar just before serving.