Preheat your air fryer to 350°F (175°C) and line a 12-cup muffin tin with paper liners.

In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt until well blended.

In another bowl, whisk together the egg, milk, vegetable oil, and vanilla extract until smooth.

Gradually fold the wet ingredients into the dry ingredients until just combined, being careful not to overmix.

Dissolve the espresso powder in the boiling water and stir it into the batter until fully incorporated.

Divide the batter among the muffin cups, filling them about two-thirds full.

Place the muffin tin in the air fryer basket and cook for 16-18 minutes, checking for doneness with a toothpick.

Once baked, let the cupcakes cool in the tin for 10 minutes, then transfer them to a wire rack to cool completely.

For the frosting, beat the softened butter and cocoa powder together in a mixing bowl.

Gradually add half of the powdered sugar and 3 tablespoons of heavy cream, mixing until smooth.

For the caramel, cook the granulated sugar in a saucepan over medium heat until it melts and turns golden brown.

Remove from heat and whisk in the diced butter, heavy cream, and vanilla extract, then allow to cool slightly.

Frost the cooled cupcakes and fill each cupcake with a generous dollop of caramel. Serve at room temperature for the best experience.