Preheat the oven to 350°F. Line a standard-size muffin tin with paper or foil cupcake liners. Spray lightly with cooking spray.
In a large bowl, whisk together the milk and vinegar and set aside for a few minutes to curdle.
Add the sugar, oil, and vanilla extract to the milk mixture and mix vigorously until foamy. Mix in the orange zest. Sift in the flour, cocoa powder, baking soda, baking powder, salt, and cayenne. Mix until no large clumps of flour are left.
Fill the lined muffin cups three-quarters of the way. Bake until a toothpick inserted into the center comes out clean, 18 to 20 minutes. Transfer to a cooling rack and let cool completely. Remove from pan when they are cool enough to handle.