Preheat oven to 350°F (177°C). Line muffin tins with paper or silicone liners.
In the bowl of a stand mixer (or in a large bowl, if using a hand mixer), combine the cake flour, the Redpath® Granulated Sugar, the Redpath® Dark Brown Sugar, cocoa powder, baking soda, and salt. Whisk together until well blended.
Using the paddle attachment, starting on low speed, beat the cubed butter into the dry ingredients until mixture looks like coarse sand and no bits of visible butter remain; 3 to 5 minutes. Speed can be increased to medium once most of the dry ingredients are coated with the butter.
In a bowl or large measuring cup, whisk together buttermilk, canola oil, eggs, vanilla extract, vinegar, and drops of red gel food colouring until mixture is homogeneous and smooth.
Make a well in the dry ingredients. Pour half of the wet ingredients into the well. Starting on low speed, and increasing to medium speed, incorporate the wet ingredients into the dry ingredients until the dry ingredients are completely hydrated. Add the remaining buttermilk mixture into the bowl. At this point, if the mixture is not a bright red, add a few more drops of red gel food colouring to the batter.
Cream the mixture on low speed until most of the liquid is combined into the batter, then increase the speed to medium-high and beat until the batter is smooth, creamy, and thick; about 1 minute.
Using a small trigger-style ice cream scoop or ladle, fill the prepared muffin tins about ⅔ to ¾ full with the batter. Place the cupcakes into the preheated oven and bake for 20 to 25 minutes. Cupcakes are done when the tops bounce back when gently pressed, or a skewer inserted into the centre comes out clean with a few moist crumbs attached.
Remove from oven and allow to cool in the pan for 5 minutes before removing and transferring to a wire cooling rack to cool completely.