Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large mixing bowl, cream unsalted butter and light brown sugar until light and fluffy.

Add the large egg and vanilla extract, mixing until fully combined and smooth.

In a separate bowl, whisk together all-purpose flour, baking soda, ground cinnamon, fine salt, and ground nutmeg. Gradually mix into the wet ingredients until blended.

Fold in old-fashioned oats and butterscotch chips using a spatula until evenly distributed.

Chill the dough in the refrigerator for about 30 minutes.

Scoop the dough into balls of about 3 tablespoons each and place on prepared baking sheets, spacing 3 inches apart.

Bake for 13-14 minutes, until edges are golden brown but centers look slightly underbaked.

Allow cookies to cool for about 10 minutes before transferring to a wire rack to cool completely.