Cupcakes:

1. Preheat oven to 350 degrees Fahrenheit.
2. Line a cupcake tin (12-mold) with paper liners and lightly spray with non-stick spray. Set aside.
3. Combine the flour, baking powder, baking soda, cinnamon, and salt in a large bowl and then set aside.
4. Combine the milk and sour cream in a small bowl and set aside.
5. Using a handheld electric mixer, beat the butter and both sugars for about 4 minutes or until light and fluffy. Add the eggs and egg yolk one at a time and beat well after each addition.
6. Reduce mixer speed and slowly add the flour mixture and milk-sour cream mixture. Add half of the flour mixture first, followed by the milk mixture, and then the remaining half of the flour mixture.
7. Add the hot water and beat until combined.
8. Fill the cupcake tins (3/4 full) and bake in the oven for about 22 minutes. Allow them to cool in the pan for 10 minutes before transferring to a cooling rack.
9. Once the cupcakes are cool enough, carve out a small hole in the middle of each cupcake, but do not discard the carved out piece.
10. Fill each hole with about 2 teaspoons of caramel sauce and then put the carved out piece back. Set aside while making the frosting.

Frosting:

1. Put a medium saucepan over medium heat and add the butter, cream, salt, and brown sugar. Cook for about 4 minutes while stirring occasionally until the sugar melts. Remove from heat and let cool for a couple of minutes.
2. Transfer the mixture into the bowl of an electric mixer. Add 2 cups of confectioner’s sugar and then beat smoothly. Increase speed and beat for 5 minutes.
3. Put the frosting in the fridge for 15 minutes. Stir then frost the cupcakes as desired.

Decoration:

1. Decorate each frosted cupcake with a drizzle of caramel sauce, a little bit of flaky sea salt, and half of a caramel candy.