Preheat oven to 350F.
Place raising into a small bowl, cover with room temperature water, and let sit for 10 minutes to plump up. Drain and set aside.
In a medium-size bowl, cream the butter and sugar using a hand mixer or a whisk. Add the egg and the vanilla extract, and keep beating until smooth.
In a separate bowl, combine the flour with salt, baking powder, cinnamon, and nutmeg. Transfer to the bowl with the creamed butter and sugar and mix well. Fold in the oats and the raisins.
Spoon the cookie dough onto a large, parchment paper-lined baking sheet, forming 8 large balls. Make sure to space the dough balls about 2 inches apart as the dough will spread a little during baking.
Place into the oven and bake until the edges of the cookies turn golden brown, about 13 minutes. The cookies will appear too soft and undercooked in the middle, but that's how they need to be. They will firm up as they cool down while staying soft and chewy.
Remove the cooking from the oven and cool on the baking sheet for 10 minutes. Transfer to a cooling rack and cool completely. Store in an airtight container for up to a week.