Preheat your oven to 350°F (180°C), and line your baking sheets with parchment paper or silicone mats, this little step keeps your cookies from sticking and makes cleanup way easier.
In a medium bowl, whisk together the flour, Dutch-process cocoa powder, baking soda, and baking powder until everything is evenly mixed.
In a large bowl, use a hand or stand mixer to cream the salted butter, brown sugar, granulated sugar, and vegetable oil until silky and fluffy.
Add in the egg, vanilla extract, and white vinegar, mixing just until incorporated. Then add the red gel food coloring and fold until the batter is a bright, festive red.
Gently fold in half of the dry ingredients, then pour in the buttermilk in a slow stream. Mix lightly until the batter begins to come together, then fold in the remaining dry ingredients until smooth. Take your time, gentle folding keeps your cookies tender and soft.
Scoop generous portions of batter onto your prepared baking sheets, leaving a little space between each. The cookies puff just enough to touch each other slightly. If you want neat, round cookies, give each scoop a gentle tap or nudge with a spoon.
Bake until the edges are set and the centers are slightly puffed, around 10-12 minutes. Let them relax on the hot baking sheet for a short while, then shift them onto a wire rack to finish cooling.
While the cookies cool, beat the butter and cream cheese together until smooth and creamy. Gradually mix in the powdered sugar, vanilla, and optional lemon juice. Whip for a few minutes until light, fluffy, and silky. Scraping the bowl a few times ensures the frosting is perfectly smooth and ready to pipe.
Pipe a generous swirl of frosting onto the flat side of one cookie, then sandwich it with another. Press lightly to secure without squishing the fluffy center, we want that soft, creamy filling to shine. Enjoy!