For the cookie dough: Warm butter in a microwave-safe bowl on 50% power for 30 seconds. Stir in cinnamon, ginger and desired spices; refrigerate butter mixture for 20 minutes. Preheat oven to 350°F. Line baking sheets with parchment paper. Cream the butter spice mixture and sugars in a large mixing bowl until light and fluffy. Add egg, egg yolk and vanilla; mix until smooth. In a separate bowl, whisk together flours, cornstarch, baking soda, baking powder and salt. Gradually add to butter mixture just until combined. Using a large cookie scoop, portion out dough into 32 balls. Place dough balls 3 inches apart on parchment-lined baking sheets. Bake for 13-15 minutes, or until lightly browned around the edges. Remove from oven and let cool on baking sheet for 5-7 minutes. Remove cookies to a wire rack to cool completely.

For the hazelnut buttercream filling: Beat the butter and hazelnut spread in a large bowl until blended. Stir in hazelnut emulsion, vanilla extract and salt. Gradually add confectioner’s sugar to butter mixture, mixing until smooth. Add heavy cream to reach desired consistency, if necessary. Fill a piping bag fitted with a star tip with buttercream. Pipe buttercream onto bottom side of 16 cookies, making stars around the perimeter of each cookie, then piping one large star in the middle. Place the remaining 16 cookies on top of filled bottom halves to make a sandwich. Pipe a small star on top the center of each completed cookie. Dust each cookie with powdered sugar.

For the toasted nut crunch: Toast the pecans and walnuts in a large skillet over medium heat for 4-5 minutes. Remove nuts from skillet and cool completely. Coarsely chop the nuts and spread evenly on parchment paper. Microwave semi-sweet chocolate in a microwave safe bowl in 30-second intervals, stirring until smooth. Stir in cinnamon and coconut oil. Drizzle chocolate over nuts and sprinkle with salt. Let cool completely. Break into 16 pieces and place on the butter cream star in the middle of each finished cookie.