Add raw cashews to a mixing bowl and cover with boiling hot water. Let rest for 1 hour (uncovered), then drain thoroughly.
In the meantime, preheat oven to 350 degrees F (176 C) and line an 8x8 inch baking dish with parchment paper. Add oats, almonds, sea salt, and coconut sugar to a high speed blender and mix on high until a fine meal is achieved.
Transfer to a medium mixing bowl and add maple syrup and melted coconut oil, starting with 4 Tbsp (60 g) and adding more if it is too dry. Stir with a spoon to combine until a loose dough is formed. You should be able to squeeze the mixture between two fingers and form a dough instead of it crumbling. If too dry, add a bit more melted coconut oil.
Transfer mixture to parchment-lined baking sheet and spread evenly. Then place parchment paper on top and use a flat-bottomed object, such as a drinking glass, to press down firmly until evenly distributed and well packed.
Bake for 15 minutes, then increase heat to 375 F (190 C) and bake for 5-8 minutes more, or until the edges are golden brown and there is some browning on the surface. Remove from oven to cool slightly, then reduce oven heat to 350 degrees F (176 C).
Once cashews are soaked and drained, add to a high speed blender with coconut cream, corn starch, lemon juice, lemon zest, sea salt, and maple syrup. Mix on high until very creamy and smooth. Taste and adjust flavour as needed by adding a bit more lemon zest and maple syrup.
Pour filling over the pre-baked crust and spread into an even layer. Tap on counter to remove any air bubbles.
Bake for 20-23 minutes or until the edges look very slightly dry and the centre appears “giggly” but not too liquid.
Let rest for 10 minutes, then transfer to refrigerator to let cool completely (uncovered) - at least 4 hours, preferably overnight.
To serve, slice and sift with icing sugar (optional). Store leftovers in the refrigerator, covered, up to 4 days, though best within the first 2 days.