In a large bowl, whisk together the hazelnut flour, fine sea salt, baking soda, spices, chopped hazelnuts and cacao nibs. In a medium bowl, stir together the butter, coconut oil, honey and vanilla extract. Combine the wet ingredients with the hazelnut flour mixture.
Roll the dough into a large log, 2½ inches in diameter, then wrap in parchment paper. Place in the freezer for 1 hour, or refrigerate a few hours until very firm.
Preheat the oven to 350°. Line 2 large baking sheets with parchment paper. Take out the log, unwrap it and cut into ¼-inch slices with a sharp, wet knife. Transfer the slices onto the prepared baking sheets, leaving 2 inches between each biscuit. Combine the Maldon salt and rapadura sugar in a little bowl and sprinkle a bit on each slice.
Bake for about 10 minutes, rotating trays once, until biscuits are golden brown. Let them rest on the baking sheets for 10 minutes, then transfer to a rack to cool completely.
Makes about 2 dozen