1 ounce (30g) cocoa butter (optional, yields a thinner coating)
Preheat oven to 300°F (150°C). Line the bottom of a 4×7-inch baking dish with parchment paper.
In a mixing bowl, combine the oat flour, almond butter, maple syrup, coconut oil, and vanilla extract. Mix until you get a slightly crumbly dough. Transfer to the prepared baking dish and press it down firmly using the bottom of a glass.
Bake for 18-20 minutes, or until golden brown. Let cool completely and keep the shortbread in the baking dish.
Creamy Hazelnut Layer
In a small bowl, whisk together the hazelnut butter, maple syrup, and tahini. Slowly pour in the melted cocoa butter and whisk gently until fully incorporated. Stir in the salt.
Pour over the shortbread base and refrigerate for at least 2 hours, or until the hazelnut layer is firmer. You can speed up the process by placing the baking dish in the freezer.
Run a knife around the edges of the baking dish. Remove the preparation from the baking dish and slice into 8 thin bars.
Melt the dark chocolate with the cocoa butter over a double boiler. Using a dipping tool, dip each bar into the melted chocolate. Place the dipped bars on a silpat or parchment paper and refrigerate 10 minutes, or let cool at room temperature to set the chocolate.
You can then wrap each bar individually with plastic film and keep at room temperature for up to 2 weeks. For a firmer hazelnut layer, keep the bars in the refrigerator.