In a medium saucepan, combine 1 cup of granulated sugar and 1/4 cup of water, stirring gently until the sugar dissolves. Heat over medium-high flame until bubbling and golden amber, about 8–10 minutes. Remove from heat and stir in 6 tablespoons of butter and 1/2 cup of heavy cream until smooth. Let cool in the fridge to thicken.

Preheat your oven to 340ºF (170ºC) and grease two 8-inch round cake pans. In a mixing bowl, sift together 2 cups of all-purpose flour, 1 tablespoon of cornstarch, 2 teaspoons of baking powder, 1/2 teaspoon of baking soda, and 1/4 teaspoon of salt. In another bowl, cream together 1/2 cup of softened butter and 1 cup of sugar until fluffy, about 3 minutes. Add 3 eggs, alternating dry ingredients with 1 cup of sour cream and 1/2 cup of vegetable oil, mixing until just combined.

Divide the batter between the pans. Bake for 20–23 minutes, or until a toothpick comes out clean. Cool in pans for 10 minutes, then transfer to a wire rack.

While cakes cool, beat 1 cup of softened butter until fluffy, about 3 minutes. Gradually mix in 4 cups of powdered sugar and 1/2 cup of cooled caramel sauce until smooth and creamy, about 2 minutes.

Once cakes are cool, place one layer on a plate. Spread buttercream on top, drizzle remaining caramel, then add the second layer. Apply a thin crumb coat and chill for 20 minutes.

Frost the entire cake with remaining buttercream. Drizzle any leftover caramel on top and sprinkle with flaky sea salt.