Heat your oven as directed by the cake mix box and line your muffin tins with 18 cupcake liners.
Take ½ cup of pretzels and crush them up—think bite-sized bits, not powder. Sprinkle these salty crumbs into each cupcake liner before adding the batter.
Prepare the chocolate cake mix according to the box instructions. Fill each liner with about ¼ cup of batter, right over the pretzel layer. Pop them into the oven and bake as directed.
While the cupcakes cool, it’s frosting time. Beat softened butter, powdered sugar, cocoa powder, milk, and vanilla until you’ve got a fluffy, chocolatey masterpiece.
Crush the remaining ¼ cup of pretzels into fine crumbs, toast them lightly in a skillet, and fold into the frosting for a subtle salted pretzel twist.
Load your buttercream into a piping bag with a star tip and swirl it onto your cooled cupcakes. Top with a sprinkle of flaked salt and a chocolate-covered pretzel. Voilà! Dessert perfection.