01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking soda, salt, cinnamon, nutmeg, allspice, and oats in a medium bowl.
03 - Beat butter, brown sugar, and granulated sugar until light and fluffy, approximately 2 to 3 minutes.
04 - Add eggs one at a time to the butter mixture, mixing well after each addition, then stir in vanilla extract.
05 - Gradually add the dry mixture to the wet ingredients, mixing just until combined.
06 - Fold in raisins and chopped hazelnuts gently.
07 - Drop dough by tablespoon or cookie scoop onto prepared sheets, spacing approximately 2 inches apart.
08 - Bake for 10 to 12 minutes until edges are golden but centers remain soft.
09 - Cool cookies on baking sheets for 5 minutes, then transfer to wire racks to cool completely.
10 - Whisk powdered sugar, hazelnut spread, and milk until smooth and pourable; drizzle over cooled cookies and let set before serving.