Preheat oven to 350 degrees. Prepare baking sheets lined with parchment paper.
Add the rolled oats to a food processor and pulse 10 times. Don’t over process, you want a variety of textures. In a large mixing bowl combine the oats, flour, baking powder, soda, salt, cinnamon and nutmeg. Whisk or stir to combine. Set aside.
In a bowl with a mixer beat the butter on medium-high about 30 seconds. Add the brown and granulated sugars and mix on medium-high until the batter lightens and becomes fluffy. Add the eggs, one at a time, beating just until the yolk disappears into the batter. Lightly beat in the vanilla. Add about 1/2 of the oat and flour mixture to the butter and egg mixture, mixing on low speed until blended. Continue adding the flour mixture until it is fully incorporated.
Using a 2 tablespoon size cookie scoop. roll the dough into balls and place on the prepared baking sheet at least 2 inches apart. I was able to fit 12 cookies on each pan. Bake for 10-12 minutes or until the bottom begin to brown. Do not over bake.
Remove the pan from the oven and let the cookies rest for 5 minutes before removing to a rack to cool completely.
To prepare the icing combing powdered sugar with the milk/cream and water. Whisk until the sugar is dissolved and the icing somewhat thick. Place the icing in a shallow dish or container. Quickly dip the tops of the cookies into the icing and let the excess drip off. Set the dipped cookie on the rack until the icing has set.
Store the cookies in an airtight container or refrigerator.