Preheat oven to 350F and line 2 baking sheets with parchment paper. Set aside.
Place butter and brown sugar in the bowl of a large stand mixer, fitted with a paddle attachment OR in a large mixing bowl with a wooden spoon. Mix on medium speed or by hand until creamy, about 2 minutes. Add maple syrup, egg, and vanilla to bowl and mix until smooth.
Combine oats, flour, baking soda, cinnamon, nutmeg, and salt in a separate medium bowl. Add to butter mixture and mix until a soft dough forms. Fold in raisins.
Use a medium cookie scoop to scoop dough out into 1-in balls. Place balls 1-2 inches apart on prepared baking sheets and gently flatten balls slightly.
Bake cookies at 350F 10-12 minutes until cookies are a light golden brown. Remove from oven and allow cookies to cool on baking sheet 10 minutes before transferring to a wire cooling rack to cool completely.