Preheat oven to 325 degrees and line a 12-cavity muffin tin with cupcake liners.
In a medium bowl, whisk together flour, baking powder, and sea salt.
In the bowl of a stand mixer or in a large bowl with a hand mixer, cream together the butter and brown sugar on medium-high speed until light and fluffy, 2-3 minutes.
Add eggs, one at a time, and beat until each is well incorporated into the mixture. Then add vanilla.
In three batches, add flour mixture alternating with buttermilk, making sure that each previous batch is incorporated before adding the next.
Fill each muffin tin about ¾ of the way with batter and bake for 23-25 minutes. Let cool in tin for a few minutes before moving cupcakes to a wire rack to cool completely.
Once cupcakes are completely cool, core out a small section from the middle (either using a cupcake corer or with a knife). Fill center of cupcake with 1-2 tsp caramel sauce. Place removed cupcake top back on if desired (not totally necessary since you'll be topping cupcake with frosting). Save any remaining filling to drizzle over finished cupcakes.
Frost cupcakes with salted caramel frosting. I used a pastry bag and Wilton 1A pastry tip for mine. Drizzle remaining salted caramel filling over cupcakes if desired.