• Preheat your oven to 350°F (175°C). Line your cupcake pans with paper liners and set them aside.
• In a medium bowl, whisk together the flour, baking powder, and salt until well combined.
• In a large mixing bowl, cream the butter and sugar together until the mixture is light and fluffy. Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
• Alternately add the flour mixture and the milk to the butter mixture, beginning and ending with the dry ingredients. Be sure to scrape down the sides of the bowl as needed, but take care not to overmix the batter.
• Evenly divide the batter among the cupcake liners, filling each about three-quarters full. Bake for approximately 20 minutes, or until the tops spring back when gently touched. Transfer the pans to a wire rack and let the cupcakes cool for 5 minutes before removing them from the pans. Allow them to cool completely.
• Once cooled, use a small paring knife to cut out a small core from the center of each cupcake. Fill the cavity with a small spoonful of caramel sauce.

For the Frosting:

• In a heatproof bowl set over a pot of simmering water (double boiler), combine the egg whites, granulated sugar, and salt. Whisk constantly over gentle heat until the sugar has completely dissolved and the mixture reaches 160°F (70°C), about 5 minutes. Be careful to heat slowly to avoid scrambling the eggs.
• Transfer the mixture to a stand mixer fitted with the whisk attachment. Beat on high speed until stiff peaks form and the mixture has cooled to room temperature, about 5 minutes.
• Reduce the mixer speed to medium and begin adding the softened butter, one piece at a time, ensuring each piece is fully incorporated before adding the next. (Note: If the buttercream appears to curdle partway through, don’t worry—just keep mixing and continue adding the butter.)
• Once all the butter has been added, switch to the paddle attachment and add ¾ cup of caramel sauce. Beat until the buttercream is smooth and well combined, about 1 minute.
• Pipe or spread the frosting onto the cupcakes, then drizzle with the remaining caramel sauce and finish with a sprinkle of sea salt.