1Melt butter in a saucepan over medium heat, stirring often, until it turns golden brown with a nutty aroma and brown bits at the bottom.
2Pour the browned butter into a heatproof bowl and let it cool until slightly warm but still liquid.
3Whisk flour, baking soda, baking powder, spices (cinnamon, nutmeg, ground cloves), and salt in a medium bowl.
4In a large mixing bowl, beat the browned butter with both light brown sugar and granulated sugar until smooth.
5Mix in the egg yolk, pumpkin purée, and vanilla extract.
6Gradually add the dry ingredients to the wet ingredients, mixing until just incorporated.
7Fold in the old-fashioned oats.
8Cover the dough and chill for 30 minutes.
9Preheat oven to 350°F and line baking sheets with parchment paper.
10Scoop 1.5 tablespoons of dough per cookie and space them apart on the baking sheets.
11Bake for 11–13 minutes, until the edges are set and the centers look slightly soft.
12As soon as the cookies come out of the oven, use a round cookie cutter or the rim of a glass to gently scoot them into perfect circles for a bakery-style look.
13Cool cookies completely on wire racks.
14Beat softened butter until creamy.
15Add marshmallow crème and beat until smooth.
16Slowly mix in powdered sugar, maple syrup, vanilla extract, and a pinch of salt. Beat until fluffy.
17Pipe or spread the maple marshmallow filling on the flat side of one cookie.
18Top with another cookie and gently press so the filling spreads to the edges.
Use a round cookie cutter or the rim of a glass to gently scoot cookies into perfect circles as soon as they come out of the oven for a bakery-style look.