Prepare the caramel by combining 1 cup of granulated sugar and 1/4 cup of water in a medium saucepan over medium heat. Stir until dissolved, then let bubble until deep amber, about 8-10 minutes. Remove from heat, whisk in 1/2 cup butter, 1/2 cup heavy cream, and a pinch of salt. Cool to room temperature.

Preheat the oven to 340ºF (170ºC) and grease three 8-inch round cake pans. In a stand mixer, beat 1 cup of granulated sugar and 1/2 cup of unsalted butter until fluffy, about 4-5 minutes. Add 3 large eggs one at a time. In a separate bowl, combine 2 cups flour, 1 tsp baking powder, 1/2 tsp baking soda, and 1/4 cup cornstarch. Alternate adding dry mixture and 1 cup sour cream, 1/4 cup vegetable oil, and 2 tsp vanilla until combined.

Divide the batter among pans and bake for 20-23 minutes. Cool in pans for 10 minutes before transferring to wire racks to cool completely.

For buttercream, beat 1 cup unsalted butter until fluffy, about 3-4 minutes. Gradually add 4 cups powdered sugar, mixing gently. Pour in 1/2 cup cooled salted caramel and 1 tsp vanilla, mixing until silky smooth.

Assemble the cake: place one layer on a serving plate, spread with buttercream and drizzle with salted caramel. Repeat with second layer, adding the final layer on top. Apply a crumb coat and chill for 15 minutes before frosting the final layer.

Frost the cake with buttercream, drizzle remaining salted caramel on top, and sprinkle with sea salt. Slice and serve at gatherings!