Pre-heat the oven to 350F (175C) and line a baking tray/sheet with baking/greaseproof paper.
Cream together softened coconut oil, honey and vanilla extract.
Add the egg and egg yolk, mix thoroughly.
In a separate bowl, sift together gluten free flour, baking powder, baking soda, salt and cinnamon. Mix in the ground hazelnuts.
Add the flour mix to the wet ingredients, and mix well until a smooth cookie dough comes together. The dough will appear a bit oily – it's supposed to be like that!
Shape individual portions of cookie dough, roughly 1 – 1½ tbsp in amount, into balls.
Place the cookie dough balls onto the baking tray, leaving about ½ inch (about 1.5 cm) between them. Flatten them (very slightly).
Bake in the pre-heated oven at 350F (175C) for about 12 minutes, or until golden brown around the edges.
Leave the baked cookies to cool before sandwich cookie assembly.