Preheat the oven to 350°F. Line a large baking sheet with parchment paper or a silicone baking mat; set aside.
Place the raisins in a small bowl and cover with water. Let them sit 5 minutes to plump. Drain the raisins and pat them dry thoroughly on paper towels; set aside.
In a large bowl, cream together the softened butter and light brown sugar until light and smooth.
Add the egg and vanilla extract to the butter mixture and beat until fully combined and smooth.
In a separate small bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, ground nutmeg, and salt.
Add the dry ingredients to the butter/sugar mixture and mix just until combined (do not overmix).
Stir in the old fashioned oats and the drained raisins until evenly distributed.
Using about 1 tablespoon of dough per cookie (or a small cookie scoop), form round portions and place them on the prepared baking sheet about 2 inches apart.
Bake for 10 to 12 minutes, until the edges are golden and the centers are still slightly soft.
Let the cookies sit on the hot baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.