For the orange buttercream frosting:
Preheat oven to 350 degrees Fahrenheit. Grease your cake pan(s) and sprinkle with flour.
Whisk together all dry ingredients in one bowl (flour, sugar, salt, baking powder, and baking soda).
Mix milk with vinegar to form curds.
In a separate bowl mix all the wet ingredients - orange juice, milk/vinegar, oil, orange zest, and vanilla extract.
Whisk about a cup of the dry ingredients into the wet ingredients. Then, stir in remaining dry ingredients.
Pour cake batter evenly into two round cake pans.
Bake for 22-25 minutes, or until a toothpick comes out clean.
Take out of the oven and let them cool in the pans for about 10 minutes and then take them out carefully unto a cooling rack.
For the frosting:
Begin to add the sugar one cup at a time. Use a spatula to bring in what goes up on the sides to have even mixing consistency.
Add in a ½ tablespoon of vegan milk at a time until it reaches your preferred volume and consistency. Stop when you are satisfied even if you have some leftover.
Beat for about 5 minutes until light and fluffy.
Once the cakes are completely cool, you can frost them by putting a small layer of frosting in between each cake and then covering it wit) frosting on the top and sides.
You can use fresh orange wedges to decorate if the cake soon before the cake is served so that they are fresh and shiny, otherwise just place the cake with the frosting in the refrigerator until ready to eat.