Line a large cookie sheet with parchment paper. Set aside.

Place the butter in a medium saucepan over medium heat. Stir occasionally until the butter has melted.

Pour the butter into a large bowl. Be sure to scrape all of the brown bits from the pan. Set aside to cool for 20 minutes.

Pulse the oats in a food processor until they are a mix of fine crumbs and larger bits. Set aside.

In a medium bowl, whisk together the flour, baking soda, cinnamon, nutmeg, and salt. Set aside.

Once the butter is cool to the touch, add the brown sugar and granulated sugar. Whisk to combine.

Add the eggs and vanilla, whisking to combine well.

Add the molasses and stir to incorporate.

Add the dry ingredients and the pulsed oats to the bowl and use a spatula to fold the ingredients together.

Using a medium cookie scoop, divide the dough into uniform scoops and place on the prepared cookie sheet. Cover and chill overnight (or at least 3 hours).

Preheat the oven to 350°F. Line two large baking sheets with parchment paper.

Remove the cookie dough from the refrigerator and transfer the dough balls onto the lined cookie sheet, leaving about 2 to 3 inches apart.

Bake one sheet at a time in the center of the oven for 8 to 10 minutes.

Remove the cookies from the oven and allow to cool on the cookie sheet for 5 to 10 minutes before transferring to a wire cooling rack.

In a medium bowl, mix all of the icing ingredients together and whisk until smooth and thick.

To ice the cookies, carefully dunk the top of each cookie in the icing without submerging it completely.