2tablespoonsplus 1 teaspoon milk,half and half or cream (more or less for desired consistency)
To prepare the cookie dough:
Preheat oven to 350 degrees F. Line a baking sheet with parchment paper and set aside.
In a medium mixing bowl combine the oats, flour, baking powder, baking soda, salt, cinnamon and pumpkin pie spice. Set aside.
Invert a large baking sheet, bottom side up on your countertop. Cover the pan with 3 layers of paper towels. Spread the pumpkin puree over the paper towels in a thin layer, using an off-set spatula. Place three more layers of paper towels on top of the pumpkin and press using your hands or the bottom of a jar, until the paper towels are soaked through.
Peel off the top layers of paper towels and discard. Flip the remaining paper towels and pumpkin paste over so the pumpkin is spread on the back of the baking sheet. Slowly peel away the remaining soaked paper towels and discard. Scrape the paste into a measuring cup. You should have 1/3 cup. If you have more, repeat the process until you only have 1/3 cup of pumpkin paste remaining.
In a large mixing bowl using an electric mixer, beat the butter on medium-high until smooth, about 30-seconds. Add the sugars and mix on medium-high until the batter lightens and becomes fluffy. Add the pressed 1/3 cup pumpkin paste, the egg, one egg yolk and vanilla to the butter mixture. Beat on medium until blended. Scrape down the sides and bottom of the bowl and beat again until well mixed.
Add 1/3 of the oat mixture to the creamed butter and pumpkin mixture. Mix on low speed just until blended. Repeat until all oats are incorporated. Scrape down the sides of the bowl with a spatula and blend one more time to ensure all the flour and oats are incorporated.
Using a 2 tablespoon size ice cream or cookie scoop, roll the dough into balls and place on the prepared baking sheet 2 inches apart. Bake for 10 to 12 minutes or just until the bottoms begin to brown. Do not over-bake. The cookies will flatten out a bit as they cool.
Allow the cookies to rest for 5 minutes then remove to a rack to cool completely.
To prepare the icing:
Whisk together the powdered sugar and milk in a shallow bowl until smooth. Quickly dip the tops of the cookies into the icing taking care not to submerge the entire top. Allow the excess icing to drip off into the bowl. Set the dipped cookies back on the rack until the icing is set.
Store the cookies in an airtight container at room temperature or refrigerate for longer storage. The cookies can also be frozen for up to 3 months. Once iced, the cookies will soften a bit over time.
The method for removing moisture from pumpkin puree adapted from America’s Test Kitchen