Boil the cashews: Add the cashews to a saucepan and cover them with water. Bring it to a boil and simmer over low-medium heat for 20 minutes while you make the cake.
For the cake
Spiced syrup: Combine the date syrup, vanilla extract, cinnamon, ginger, nutmeg, and salt in a large mixing bowl.
Oats & almonds (optional): If needed, blend the oats and the almonds in a blender until finely ground.
Carrots: Peel and grate the carrots. If using pre-shredded carrots, give them a rough chop to cut long strings into smaller pieces.
Combine: Add the oat flour, almond flour, and grated carrots to the mixing bowl. Combine everything with a spatula.
Set: Line an 8x8" (20x20 cm) square pan with parchment paper. Firmly press the carrot cake mixture into the pan. Smooth out the surface with wet fingers. Place it in the fridge to set while you make the frosting.
For the frosting
Cocoa butter: Melt the cocoa butter over low heat or in the microwave in 30-second intervals at 650W.
Blend: Add the drained cashews, melted cocoa butter, maple syrup, vanilla extract, lemon juice, and plant-based milk to a high-speed blender. Blend until perfectly smooth (it can take up to 3 minutes).
Set: Pour the frosting over the carrot cake. Place in the fridge to set for at least 6 hours or preferably overnight.