Center a rack in the oven and preheat to 350 (F). Prepare a 6 x 3-inch cake pan by spraying generously with cooking spray and lining the bottom with a parchment paper circle. Spray the parchment paper with cooking spray. Set aside.
In a medium bowl, combine 1/2 cup plus 2 tablespoons all-purpose flour, 1 1/2 teaspoons natural unsweetened cocoa powder, 1/2 teaspoon baking soda, and 1/4 teaspoon kosher salt. Whisk together until combined. Set aside.
In a freestanding electric mixer fitted with a paddle attachment, combine 1/4 cup vegetable oil and 1/2 cup granulated sugar. Beat together on medium-high speed until pale and fluffy, about 3 to 4 minutes. Lower the mixer speed to its slowest setting and add 1 large egg. With the mixer still on its lowest speed, add 1 1/2 teaspoons red food coloring, 3/4 teaspoon pure vanilla extract, and 1/4 teaspoon white vinegar and continue to mix the batter until the red food coloring is fully incorporated. Once the batter is a vibrant red, keep the mixer speed on its lowest setting and add the dry ingredients (from the 2nd step) in three parts, alternating with 1/4 cup buttermilk in two parts, starting and ending with the dry ingredients. Once the last of the dry ingredients have been added, increase the mixer speed to medium and beat for 1 minute, before turning off the mixer completely. DO NOT OVERMIX OR YOUR CAKE WILL BE TOUGH AND I WILL CRY.
Scoop the batter into the prepared cake pan and bake for 25 to 30 minutes, or until a wooden toothpick inserted into the center comes out clean and the top of the cake bounces back when slightly prodded. Transfer to a wire rack to cool completely.