Preheat the oven to 350°F and line a 12-cup muffin pan with liners. Stir the almond milk and vinegar together and let it sit for 5 minutes to create a dairy free buttermilk.
Whisk the flour, sugar, baking powder, and salt in a large bowl.
Whisk the oil, eggs, and vanilla into the milk mixture, then pour it into the dry ingredients and stir just until smooth. Do not overmix.
Divide the batter among the liners, filling each about 2/3 full, and bake for 18 to 20 minutes until a toothpick comes out clean.
Cool the cupcakes completely on a wire rack. Even slightly warm cupcakes will melt the frosting.
Beat the vegan butter for 2 minutes until pale and creamy. Gradually add the powdered sugar, then the vanilla, salt, and enough almond milk to reach a fluffy, pipeable consistency, whipping for 2 more minutes.
Pipe or swirl the frosting generously onto the cooled cupcakes and finish with sprinkles if you like.