Pumpkin Oatmeal Sandwich Cookies

Notes

12 cookie sandwiches (i.e., 24 cookies plus filling).

Heat oven to 350 ºF and line two large rimmed baking sheets with parchment paper. Place your racks in the top and bottom third of the oven.
Using a large bowl and electric mixer, cream the butter, brown sugar and granulated sugar until light and fluffy, 5 minutes. Mix in the pumpkin purée, pumpkin spice, vanilla and salt until well combined.
Add the oats, flour and baking soda and mix on low speed until moistened, then switch to a flexible spatula to mix just until combined.
Scoop the dough in heaping tablespoons onto the prepared baking sheets, leaving about 2 inches between scoops. Use damp fingers to gently press and slightly flatten each portion; they will not spread much.
Bake 14 to 16 minutes or until the cookies are matte and slightly golden on the edges, rotating the pans from front to back and switching racks halfway through. Cool completely on the baking sheets.

While the cookies cool, prepare the frosting (if using): In a medium bowl, combine the butter, powdered sugar, pumpkin purée, pumpkin spice, vanilla and salt. Mix on low with an electric mixer until the sugar is moistened, then adjust speed to medium-high and mix until light and fluffy, scraping the bowl as necessary, about 3 minutes. Transfer to a large piping bag.
Pair up cookies into sets of same-size/same-shape cookies. Pipe a generous dollop of filling onto one cookie, then press into the other to create a sandwich and to have the filling spread to the edges.
Store frosted cookies in an airtight container, layering with parchment or wax paper, and keep in the fridge or at room temperature.