In a medium saucepan, melt sugar over medium-high heat. When the sugar starts melting, whisk until all the sugar melts. Sugar will clump in whisk but keep whisking.

Once all the sugar is melted, stop whisking and let the sugar get to a deep amber color. You can swirl the pan to mix. Keep your eye on the caramel, as it will easily burn at this stage.

Whisk in the butter and mix until completely melted. Remove pan from heat and gradually add in the heavy cream. Whisk until smooth. Whisk in the sea salt (if using) and whiskey. Transfer caramel immediately into a glass jar and let cool.

Preheat oven to 350 degrees. Prepare two muffin tins with cupcake liners.

In the bowl of a stand mixer (or large mixing bowl), using the whisk attachment, whip the butter on medium-high speed for two minutes. Gradually add the sugar with the mixer going and cream together until light and fluffy, about 5-6 minutes. Add in the eggs, one at a time, and mixing until combined between each addition.

In a small bowl, whisk together the cake flour, baking powder, baking soda, and salt. Reduce the speed to low and add in the flour mixture in two additions. Mix on low until just combined. Add in the sour cream, vegetable oil, vanilla extract, and whiskey. Beat until incorporated.

Divide batter evenly into prepared cupcake liners, filling each ⅔ full and bake cupcakes until a tester inserted into the middle comes out almost clean, about 12-15 minutes.

Remove cupcakes from the oven and transfer to a wire cooling rack and let cool completely.

Whip butter on medium speed for about 2-3 minutes in the bowl of a stand mixer fitted with the paddle attachment until light and creamy.

Add the powdered sugar and whiskey caramel and mix on low for 1 minute until combined.

Increase speed to medium-high and whip for 4-5 minutes until light and fluffy.

Using a pastry bag fitted with your decorating tip (I used Wilton 1M), frost the cupcakes with the frosting.