1. Adjust the oven racks to the low and middle positions and heat the oven to 350 degrees. Line 2 large baking sheets with parchment paper or spray them with nonstick cooking spray.

2. Whisk the flour, baking powder, salt, and cinnamon together in a medium bowl.

3. Either by hand or with an electric mixer, beat the butter on medium speed until creamy. Add the sugars; beat until fluffy, about 3 minutes. Beat in the eggs, 1 at a time.

4. Stir the dry ingredients into the butter-sugar mixture with a wooden spoon or large rubber spatula. Stir in the oats.

5. Working with a generous 2 Tablespoons of dough each time, roll the dough into 2-inch balls. Place the balls on the prepared baking sheets, spacing them at least 2 inches apart.

6. Bake until the cookie edges turn golden brown, 22 to 25 minutes, rotating the baking sheets front to back and top to bottom halfway through the baking time. Let the cookies cool on the baking sheets for 2 minutes. Transfer the cookies with a wide metal spatula to a wire rack. Let cool at least 30 minutes.

7. To make the frosting: Combine the butter and confectioners sugar in the bowl of your stand mixer. Mix on low speed at first, then increase the speed until combined. Add in your heavy cream and vanilla extract, and mix on medium to high speed for 8 minutes until light and creamy. If not using immediately, store in a container in the refrigerator until ready to use, mix again until light and fluffy. Otherwise, spread a nice thick layer of frosting on each cookie and enjoy!