Soak cashews in boiling water for 30 minutes.
Drain well.
Add cashews, vanilla, lemon juice, coconut cream or plant milk, and maple syrup to a food processor.
Blend until smooth and creamy.
Spread over the chilled brownie layer.
Return to the freezer for 1–4 hours.
Remove from the freezer, slice into bars, add optional toppings, and enjoy!
Optional toppings: chocolate chips, shredded coconut, chopped nuts, cacao nibs, cocoa powder, or flaky sea salt.