Preheat oven to 350℉ (176℃) and grease an 8 x 8 square pan with spray.
Sift cake flour, cocoa powder, baking soda, baking powder, and salt into a bowl. Set aside.
1 cup + 3 tablespoons cake flour (137.4 grams), 1/2 tablespoon cocoa powder, 1/2 teaspoon baking soda, 1/4 teaspoon baking powder, 1/4 teaspoon salt
In a separate bowl, whisk together granulated sugar with oil. Then add buttermilk, vinegar, an egg, vanilla extract and food colouring. Mix until combined.
1/2 cup granulated sugar (100 grams), 1/3 cup canola oil, 1/2 cup buttermilk, 1 teaspoon distilled white vinegar, 1 large egg, 1 teaspoon vanilla extract, 3 to 5 drops red gel food coloring
Add in the dry ingredients and fold together until incorporated (avoid over-mixing). Pour the batter into the baking pan and bake for 15 to 18 minutes or until a toothpick comes out clean. Allow the cake to cool in the pan for 10 minutes and then transfer it to a wired cooling rack.