Preheat oven to 350°F. Prepare a cupcake tin by placing baking liners into each of the cups.
In a small bowl, slowly mix the oil, vinegar, and vanilla into the dairy-free milk, allowing it to curdle. In a large bowl, sift together the flour, sugar, baking powder, baking soda, and salt.
Pour the liquid mixture over the flour mixture and stir gently, being very careful not to over-mix. Once combined, spoon the batter into each of the lined cupcake cups, filling each about ⅔ of the way full.
Bake for 20-25 minutes or until a toothpick inserted into the center of a cake comes out clean. Remove from oven and allow to cool for a few minutes in the tray. Once cool enough to touch, remove from the tray and cool the rest of the way on a cookie rack.
Buttercream Frosting: While the cupcakes are cooling, prepare the buttercream. Start by whipping the vegan butter with an electric mixer or by hand until slightly soft and smooth. Add the powdered sugar, 1 cup at a time. Add the full 4 cups for a sweeter and stiffer frosting.
Mix in the vanilla, salt, and a little bit of the dairy-free milk until your desired consistency is reached. Spread or pipe the frosting onto the completely cooled cupcakes in whatever fashion you like and enjoy.