Low carb Chocolate Hazelnut Shortbread Sandwich Cookies

cookies (makes 24 single cookies or 12 sandwich cookies) 75g unsalted butter (softened not melted) 50g powdered erythritol 3, 4 tsp vanilla 135g almond flour 30g crushed toasted hazelnuts pinch salt 1, 4 tsp xanthun gum chocolate ganache filling 100g unsweetened dark chocolate 1 cup heavy cream 1 teaspoon powdered erythritol