Preheat the oven to 350F.
If the hazelnuts are not roasted and peeled, roast them for 5-6 minutes at 350F and peel them afterward.
Ground the hazelnuts with a blender until you have a smooth mixture.
In a large mixing bowl, mix the eggs, honey, melted coconut oil, and the vanilla.
In a separate bowl, mix the dry ingredients. Mix the flours, starch, baking powder, salt, and hazelnuts.
Slowly add the dry ingredients to the wet ingredients and stir well.
This will form a dough, which might be a bit oily. If the dough feels too sticky, leave the dough in the fridge or freezer for about 10 minutes.
Form small cookies (around 1 tablespoon from the mixture) and place them on baking paper.
Flatten them gently on top.
Place the cookies in the oven at 350 F. Bake the cookies for 10 minutes.
In the meantime, prepare the filling. You can also use a pre-made spread such as Nutella.
Mix the hazelnut butter with cocoa powder and the honey. Add ground hazelnuts in order to thicken the mixture. It will be a bit hard to work with but it needs to have a thicker consistency.
Once the cookies are done and cooled completely, spread the chocolate filling on the cookie with the help of a spoon or your hand - it should be thick enough to form it with a hand. Place a second cookie on top and squeeze gently.
In a separate bowl mix the hazelnut butter and cocoa powder for the decorative topping.
Gently dip the cookie sandwiches in the chocolate spread and then sprinkle with ground hazelnuts.