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

In a medium bowl, whisk together the all-purpose flour, baking powder, salt, cinnamon, and nutmeg until well combined.

In a large mixing bowl, use an electric mixer to beat the softened unsalted butter and brown sugar together until light and fluffy, about 2-3 minutes.

Add the large egg and vanilla extract to your butter-sugar mixture and mix on medium speed until fully incorporated.

Gradually pour in the milk while mixing on low speed until smooth and well combined.

Slowly add the flour mixture to the wet ingredients, mixing on low until just combined.

Fold in the old-fashioned rolled oats until evenly distributed throughout the dough.

Gently mix in the white chocolate chips until evenly dispersed throughout the dough.

Drop rounded tablespoons of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Lightly press down on each dough ball to slightly flatten them, about half an inch thick.

Bake for 10-12 minutes until the edges turn golden brown and the centers are set.

Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.