Preparation:

Step 1: Prepare the Cupcake Batter

1. Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
2. In a medium bowl, whisk together the flour, baking powder, and salt.
3. In a separate large bowl, beat the butter and sugar together until light and fluffy (about 2-3 minutes).
4. Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
5. Gradually add the dry ingredients to the wet mixture, alternating with milk, and mix until just combined.
6. Fold in the caramel sauce until fully incorporated.

Step 2: Bake the Cupcakes

1. Spoon the batter into the cupcake liners, filling each about 2/3 full.
2. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
3. Remove from oven and let the cupcakes cool completely before filling and frosting.

Step 3: Make the Caramel Filling

1. In a small bowl, mix the caramel sauce and sea salt until smooth.
2. Using a cupcake corer or a small knife, create a small hole in the center of each cupcake.
3. Fill each hole with a spoonful of the caramel filling.

Step 4: Prepare the Buttercream Frosting

1. In a large bowl, beat the butter until creamy and smooth.
2. Gradually add powdered sugar, beating well after each addition.
3. Mix in the caramel sauce, vanilla extract, and salt.
4. If needed, add heavy cream one tablespoon at a time to achieve the desired consistency.

Step 5: Decorate the Cupcakes

1. Pipe the frosting onto each cupcake using a star-shaped piping tip.
2. Drizzle additional caramel sauce over the frosting.
3. Sprinkle with flaky sea salt and top with a caramel candy if desired.