To make the base layer, place all the ingredients in a food processor and combine for 10 seconds, until it's combined but still has visible chunks of hazelnuts in it. Transfer to a foil-lined 5"x 3" container.
Place in the fridge while you make the filling.
To make the filling, place all the ingredients in a bowl set over a pan of simmering water (a double boiler), then stir well when everything's melted to form a smooth, dark mixture. Taste and add more maple syrup if necessary.
Remove the base layer from the fridge, then pour the filling over the base and smooth over with a spatula. Transfer to the fridge for 10 minutes to let it firm up just a little.
To create the crunchy hazelnut layer, sprinkle the chilled filling evenly with the crunchy roasted chopped hazelnut pieces. Melt the chocolate and coconut oil in double boiler or in the microwave, then drizzle the chocolate evenly over the hazelnut pieces. Finally, transfer the container to the fridge and let firm up for at least 8 hours.
Using the foil, remove from the container. With a sharp knife, cut into sixteen small squares. Serve immediately or place in an airtight container and store in the fridge until you're ready to eat them - they melt fast!