Chewy, caramel-sweet oatmeal cookies made with sourdough discard are sandwiched around a fluffy vanilla buttercream-cream cheese filling. Nostalgic and decadent, they balance warm spice and tangy depth with a soft, tender bite.
Preheat oven to 350°F. Line baking sheets with parchment paper.
In a stand mixer, cream softened butter, brown sugar, and granulated sugar with the paddle attachment, scraping the bowl as needed.
Add eggs one at a time, then mix in vanilla and sourdough discard until well combined.
In a separate bowl, whisk together oats, all-purpose flour, baking soda, baking powder, cinnamon, and salt.
Add dry ingredients to the wet mixture in about 3 additions, mixing just until combined after each. Do not overmix.
Scoop about 36 dough mounds onto prepared sheets, spacing about 2 inches apart.
Bake 10 minutes, until edges are golden and centers appear slightly underdone. Cool on the tray 2 minutes, then transfer to a rack to cool completely.
Make the frosting: In a clean mixer bowl, beat room-temperature butter and cream cheese with the whisk attachment until smooth and creamy.
Add vanilla and salt. With mixer on low, gradually add powdered sugar; then whip on medium-high until light and fluffy.
Assemble: Pipe or spread frosting onto the flat side of one cooled cookie; top with a second cookie to form a sandwich. Repeat with remaining cookies and serve.