Brown Butter
1-Using brown butter is optional, but it: Using brown butter is optional, but it gives these cookies such a deliciously warm, toasted flavor! However, if you’re short on time, you can always just use regular butter.
2-Grab a wide, heatproof bowl to pour: Grab a wide, heatproof bowl to pour the butter into once it’s browned. Set aside.
3-Place 1 cup of unsalted butter in: Place 1 cup of unsalted butter in a large, light-colored pan (to make it easier to see) over medium heat. Stir the butter the entire time with a rubber spatula to prevent the milk solids from burning!
4-Once melted, the butter will foam and: Once melted, the butter will foam and sizzle around the edges. Keep stirring!! The butter should turn golden brown after 5-6 minutes and be topped with a foamy layer of bubbles. Shortly after this the foam should kind of fade away and the milk solids at the bottom of the pan will be a perfectly toasted brown. It should have a strong, nutty aroma.
5-Immediately remove the pan from heat and: Immediately remove the pan from heat and pour the butter into a heatproof bowl to stop the cooking process. If left in the hot pan, the milk solids will burn. It can happen in a flash, trust me!! Place the brown butter in the fridge for 30 minutes to cool to room temperature.

Oatmeal Cookies
6-Preheat the oven to 350°F/175°C and line: Preheat the oven to 350°F/175°C and line two large baking sheets with parchment paper or silicone baking mats. Set aside.
7-Add 1/2 cup of room-temperature brown butter: Add 1/2 cup of room-temperature brown butter (the remaining amount will be used to make the frosting) and 1 cup packed dark brown sugar into a large bowl or the bowl of a stand mixer fitted with a paddle attachment. Beat on a medium-high speed for a couple of minutes, or until the mixture becomes lighter in color and looks fluffy. Scrape the sides and bottom of the bowl as needed with a rubber spatula.
8-Next, scoop 1/4 cup of pumpkin puree: Next, scoop 1/4 cup of pumpkin puree onto a couple of sheets of paper towel and pat it to remove any excess moisture. Then add the blotted pumpkin puree and 1 tsp vanilla extract to the butter/brown sugar mixture. Mix on a medium speed until combined.
9-Then fold 1 1/4 cups all-purpose flour,: Then fold 1 1/4 cups all-purpose flour, 3/4 cup old-fashioned oats, 1 tsp baking soda, 1/2 tsp ground cinnamon, and 1/2 tsp fine salt into the wet ingredients with a rubber spatula or wooden spoon until just combined. Scrape the sides and bottom of the bowl as needed to make sure everything is properly mixed together. The dough should be quite thick.
10-Use a 1 Tbsp cookie scoop or: Use a 1 Tbsp cookie scoop or a small spoon to measure about 32 cookie dough balls and place them on the prepared pans. Space them about 1 1/2 inches apart, as they’ll spread a bit as they bake.
11-Bake one tray at a time on: Bake one tray at a time on the middle rack of your oven for 8-9 minutes, or until the edges look set and the centers have puffed up but are still soft.
12-Gently flatten the cookies with the bottom: Gently flatten the cookies with the bottom of a metal measuring cup or glass while they’re still warm. Then let the cookies cool on the sheet for 10 minutes, then place them on a wire rack to finish cooling.

Brown Butter Cream Cheese Filling
13-While the cookies bake and cool, make: While the cookies bake and cool, make the brown butter cream cheese filling. I prefer making it with a hand mixer because this makes a pretty small amount of frosting.
14-In a medium bowl, beat 1/3 cup: In a medium bowl, beat 1/3 cup of room temperature brown butter (should be the amount remaining) and 1/4 cup room temperature cream cheese together on a medium-high speed until combined.
15-Then add 1 cup powdered sugar, 1: Then add 1 cup powdered sugar, 1 tsp vanilla extract, and 1/4 tsp fine salt. Mix on a low speed until combined and smooth. Scrape the sides and bottom of the bowl as needed with a rubber spatula.
16-Scoop the frosting into a large piping: Scoop the frosting into a large piping bag or a freezer ziplock bag, and cut an opening at the base that’s about 1/2 inch wide.
17-Pair the cookies up (it’s ok if: Pair the cookies up (it’s ok if they’re not all exactly the same size!), then pipe a generous layer of frosting on the back of one of the cookies before sandwiching them together. Repeat until all the cookies are filled, then enjoy! These can sit out at room temperature for a few hours, or be stored in an airtight container in the fridge for up to a week.