Preheat oven to 350°F (175°C) and line muffin tins with cupcake liners.
In a bowl, whisk together flour, baking powder, and salt. Set aside.
Beat butter and sugar until light and fluffy.
Add eggs one at a time, mixing well after each.
Stir in vanilla extract.
Alternately add dry ingredients and milk, mixing until just combined.
Fill cupcake liners ⅔ full with batter.
Bake for 18-20 minutes or until a toothpick comes out clean.
Cool cupcakes in pan for 5 minutes, then transfer to a wire rack.
Heat sugar in a saucepan over medium heat, stirring constantly.
Stir in butter until melted.
Slowly whisk in heavy cream (mixture will bubble).
Remove from heat and stir in sea salt. Let cool.
Beat butter for buttercream until creamy.
Gradually mix in powdered sugar.
Pour in salted caramel sauce and mix well.
Add heavy cream as needed for desired texture.
Use a cupcake corer or knife to remove cupcake centers.
Spoon cooled salted caramel into each cupcake.
Pipe caramel buttercream onto cupcakes.
Drizzle caramel sauce and sprinkle with sea salt.