Preheat oven to 350°F/175°C. Line two muffin pan compartments with cupcake papers, or spray each compartment with vegetable spray.
Combine in a large mixing bowl the flour, sugar, cocoa, salt baking soda, and cornstarch. Stir to combine.
In a smaller bowl, combine the vegetable oil, water, vinegar, and vanilla. Stir to combine.
Pour the water mixture into the flour mixture and gently fold until just combined. Do not overmix.
Pour the batter into prepared muffin tins. Bake for 20 to 25 minutes until a toothpick inserted in the middle comes out clean.
Allow the cupcakes to cool for about 2 to 3 minutes and then remove them from the cupcake pans. Allow them to cool completely before frosting.
Make-Ahead Tips: After cupcakes are baked, cool them completely, and cover in an airtight container. They can be stored overnight at room temperature. You can also prepare the frosting the day before. I actually put it in the pastry bag, place that bag in a freezer bag, and then refrigerate it. Be sure to let it sit at room temperature for about 15–20 minutes before frosting the cupcakes.I find the batter for vegan cupcakes is best if it's a little on the thick side. Runny batter will create cupcakes that are flat on the top. They'll still taste fine! So, this batter will be a little thicker than a traditional cupcake batter.Nutrition estimate is for the cupcakes without frosting.