Soak raw cashews in cold water overnight, or in boiling water for 1 hour (uncovered). Drain thoroughly.
Preheat the oven to 350°F and line an 8x8 inch baking dish with parchment paper.
In the bowl of a food processor (or blender), add the almonds, walnuts, oats, maple syrup, shredded coconut and sea salt, and blend until mixture is crumbly and sticky, about 2 minutes.
Transfer the mixture to the baking dish, and spread evenly. Use the back of a spoon or measuring cup to press down firmly until it’s evenly distributed and well-packed.
Bake in the preheated oven for 20 minutes, until the edges are golden brown. Remove from oven and cool slightly.
Wipe down the food processor. Then, transfer the drained cashews to the bowl of the food processor along with the coconut cream, corn starch, lemon juice, lemon zest, sugar, turmeric (optional) and sea salt.
Mix on high until well blended and smooth. Pour the filling over crust and spread evenly.
Bake for another 20 minutes, or until the edges look firm and the center appears slightly “jiggly.” Allow the baking dish to cool on the counter, then transfer to a refrigerator to cool (uncovered) overnight, or at least 4 hours.
Cut into 9 large slices or 16 smaller slices. Sprinkle powdered sugar on top (if desired).