Start by melting and lightly browning butter on stovetop. To do this, add butter to a saucepan and turn on to medium heat. It will begin melting, then turn to a simmer and sputter. It will then turn to a foaming, continue stirring. You will then start to smell a nuttiness and see little bits of brown specks accumulating on the bottom of the pan. Remove from heat and pour into a large glass bowl to cool.
After 8 minutes, whisk in brown sugar and pumpkin puree. Then whisk in egg yolk, molasses, and vanilla.
In a separate bowl, whisk together almond flour, oat flour, tapioca starch, baking soda, baking powder, salt, cinnamon, and nutmeg. Fold dry ingredients into wet, and once no flour streaks remain, make 20 aggressive stirs.
Refrigerate dough for 30 minutes.
Meanwhile, preheat oven to 350 degrees F.
Scoop dough into 50 gram dough balls, about 2 tablespoons. The dough will be sticky, and that's okay. Put 8 cookies onto a parchment lined baking sheet.
Bake for 13 minutes, until cookies are just set. Let cool on pan for 5 minutes, then move to a wire rack to finish cooling.
Once cookies are completely cooled (important for icing), whisk icing ingredients together until smooth. Drizzle onto cookies.
Cookies will keep well in a closed container for up to five days.