Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.
In a large bowl, cream together the melted butter, brown sugar, and granulated sugar until smooth.
Beat in the egg and vanilla extract until light and fluffy.
In a separate bowl, whisk together the flour, baking soda, cinnamon, nutmeg, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the rolled oats and raisins until evenly distributed.
Drop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches between each cookie.
Bake for 9-11 minutes, or until the edges are golden brown and the centers are still slightly soft.
Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.