Preheat the oven to 350. Lightly spray cupcake pan with cooking spray and line it with cupcake liners.

In a small sauce pot, mix water with unsweetened cocoa powder. Bring to a low boil. Cook for about a minute and set aside to cool.

In a bowl of an electric mixer, combine flour, sugar, baking powder, baking soda and salt. Mix until combined.

Separately, whisk together vegetable oil, vanilla extract, eggs and sour cream.

On low speed, slowly pour in the egg mixture into the dry ingredients. Once it's combined, bring the speed up to medium and beat for about two minutes.

Lower speed to low again and slowly pour in cocoa mixture. Mix until just combined. Turn off mixer.

Using a spatula, scrape sides and bottom of the bowl, continue mixing with a spatula until batter is smooth.

Pour batter into the cupcake liners, filling them about ¾ of the way, and bake for 18-20 minutes. Do a toothpick test at 18 minutes to check for doneness.

Cool to room temperature before filling and frosting.

Using a small cookie dough scoop (number 50), scoop out some of the cupcake on top and then, using the same size scoop, fill each cupcake hole with dulce de leche.

Sprinkle a little bit of coarse salt over each cupcake.

(You can make cake pops or cake truffles with the scooped out chocolate cake.)

Warm the chocolate in a double boiler or in the microwave until melted and allow to cool slightly.

Beat butter until it is fluffy (about 3-5 minutes) on high speed. Scrape sides and bottom of the bowl. On low speed add powder sugar and egg yolk alternately, beating after each addition.

The mixture should be very fluffy.

With the mixer on medium low, gradually drizzle in melted chocolate.

Transfer the frosting to the pastry bag and frost the cooled, filled cupcakes.

Sprinkle some coarse salt on top of frosting too.