Preheat oven to 325 degrees then line a muffin tin with 12 cupcake liners. In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt and cocoa powder until well combined and all of the lumps of flour and cocoa are smooth.
In a separate smaller bowl, mix together oil, milk, beaten egg and vanilla. Pour wet mixture into the larger bowl containing dry ingredients then stir until dry ingredients are just moistened then set aside.
Heat water to boiling (microwave is fastest). Add boiling water to batter then stir carefully until completely combined. Pour batter into muffin tin, filling each cup about ¾ full.
Bake 16–18 minutes or until center is barely firm and tops begin to achieve a ‘crackled’ look. Remove from oven then place on a rack to cool completely.
While cupcakes cool, prepare frosting by placing a small saucepan over medium heat. Add butter, brown sugar and cream then heat just until sugar has dissolved. Remove from heat, stir in vanilla and salt then let mixture cool.
Transfer cooled frosting mixture to a large mixing bowl or stand mixer fitted with whip attachment.
Beat frosting mixture on low speed then add powdered sugar slowly in increments. Check consistency of frosting after all 3 cups have been added. Adjust frosting to desired thickness by beating in powdered sugar a little bit at a time.
Top each cupcake with a bit of frosting, drizzle with chocolate and caramel sauce, if you like. Sprinkle with kosher salt.