Soft oatmeal cream pies with fluffy marshmallow filling sandwiched between chewy oatmeal cookies are a nostalgic family treat. These homemade versions far surpass the lunchbox classics.
Preheat your oven to 350°F and line two baking sheets with parchment paper for even baking and easy removal.
In a medium bowl, whisk together flour, baking soda, salt, and ground cinnamon for consistent flavor and leavening.
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar on medium speed for 2 minutes until pale and fluffy.
Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next; add vanilla extract and mix just until combined.
Stir the dry ingredients into the wet ingredients in two additions, mixing on low speed after each just until no flour streaks remain.
Fold in the oats by hand to avoid overmixing, which helps keep the cookies chewy.
Drop heaping tablespoons of dough 2 inches apart on prepared sheets, then bake for 10-12 minutes until edges are set but centers remain soft—do not overbake for a chewy texture.
Cool cookies on sheets 5 minutes, then transfer carefully to a wire rack and cool completely before filling.
For the cream filling, beat together shortening, powdered sugar, marshmallow creme, salt, and milk on medium-high until fluffy and smooth.
To assemble, spread 2 tablespoons of filling on the flat side of half the cookies and gently sandwich with the remaining cookies; let set 15 minutes for best texture.