Butter and flour two 9-by-2-inch round cake pans or line a cupcake tray with paper liners. In a medium sized bowl, combine the flour, salt and cocoa powder. Set aside.
In another bowl, mix together the sugar and oil until well combined. Add in the 2 eggs and beat well. Next, stir in the food colouring and the vanilla. Add in half of the flour/cocoa mixture, alternating with the yogurt, scraping the sides of the bowl with a rubber spatula as needed.
In a small bowl, mix baking soda and vinegar until combined. Add to batter, and beat for 10 seconds. Divide batter between the prepared pans (if using) or pour batter 3/4 full into the cupcake liners.
Bake for 30 to 35 minutes, or until a toothpick inserted into the centre of the cake comes out clean. Cool for about 5 minutes before removing from pan, then place on wire racks to cool completely. Frost or cover in whipped cream as desired.