01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - Whisk together flour, oats, baking soda, salt, cinnamon, and nutmeg in a medium bowl.
03 - Beat butter, brown sugar, and granulated sugar until light and creamy, approximately 2-3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
05 - Gradually add dry ingredients to wet mixture, stirring until just combined.
06 - Fold in raisins and chopped hazelnuts until evenly distributed.
07 - Drop tablespoon-sized scoops of dough onto prepared baking sheets, spacing 2 inches apart.
08 - Bake for 11-13 minutes until edges are golden brown and centers are just set.
09 - Let cookies cool on baking sheets for 5 minutes, then transfer to wire rack to cool completely.
10 - Warm hazelnut spread and heavy cream together in microwave-safe bowl for 20-30 seconds. Stir until smooth.
11 - Drizzle hazelnut mixture over cooled cookies using spoon or piping bag. Allow to set before serving.