Preheat oven to 350°F and line muffin tins with cupcake liners.
In a bowl, mix flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add vanilla, eggs, milk, and oil. Mix on low to combine, then on medium for 1 minute.
Fill cupcake liners ½–⅔ full. Bake for 14–16 minutes. Cool completely.
For frosting: Beat butter, cocoa, salt, and half the sugar. Add rest of sugar, milk, vanilla. Beat until fluffy.
Melt chocolate chips and transfer to a piping bag.
Pipe frosting on cupcakes, drizzle with melted chocolate, and top with a Ferrero Rocher.