Preheat oven to 350°F and line an 8x8” square pan with parchment paper. Grease with nonstick cooking spray.
In a mixing bowl, stir together the hazelnut flour, tapioca flour, coconut sugar, salt, and melted coconut oil until fully combined, and there's no dry flour remaining. Press the crust evenly in the pan.
In your food processor or blender, grind the hazelnuts, tapioca flour, salt, and coconut sugar to a powder (or as fine as you can make it). Add the coconut oil and process until no longer visible. Add the egg and vanilla, blending until completely incorporated, and a smooth paste is formed. Spread the filling evenly over the hazelnut crust.
Top the filling with chocolate chunks and hazelnuts and press them into the chocolate hazelnut mixture.
Bake for 15-18 minutes, or until just barely set and a skewer inserted into the center comes out clean - be careful not to over-bake or they'll be dry!
Let cool completely before cutting into squares. Keep any leftovers in an airtight container.