Preheat your oven to 350 degrees F.
Whisk together the first 7 dry ingredients in a large mixing bowl.
Make 3 depressions or shallow dips in the dry cake batter mixture, 2 small and 1 large.
Pour the vinegar in a small depression, the vanilla extract and chocolate stevia in the other small depression and the oil in the large depression.
Pour the water over the top and stir the wet ingredients into the dry until smooth.
Spread the batter into the baking pan. Sprinkle optional sugar free chocolate chips over the top of the cake mix if using.
Place in the middle rack of your oven and bake for 30 minutes or until a toothpick in the center comes clean.
Allow to cool for 10 minutes then remove by holding the ends of the parchment paper.
Place onto a cutting board to frost then slice. Store: Allow to cool completely then cover with plastic wrap and place in the fridge for up to 3 days to ensure moistness.