Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.

In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.

Add the egg, milk, vegetable oil, and vanilla extract to the dry ingredients and mix until smooth.

Stir in the boiling water carefully, knowing the batter will be thin.

Pour the batter evenly into the lined muffin tin, filling each cup about two-thirds full.

Bake the cupcakes for about 18-20 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cupcakes to cool completely before frosting.

In a medium saucepan over medium heat, melt the sugar, stirring constantly until it turns amber.

Add the cubed butter and stir until combined.

Carefully pour in the heavy cream and add sea salt, stirring until smooth. Let it cool slightly.

Top the cooled cupcakes with the salted caramel sauce and sprinkle with sea salt or chocolate chips if desired.