Place racks in the center and upper third of the oven and preheat to 350 degrees F.  Line two cupcake pans with paper or foil liners.  Set aside.

In a medium bowl, whisk together flour, cornstarch, baking powder, baking soda and salt.  Set aside.

In the bowl of an electric stand mixer fitted with a paddle attachment, add butter and sugars.  Beat on medium speed until fluffy and pale brown, about 3 minutes.   Stop the mixer, scrape down the sides of the bowl and add one egg.  Beat on medium for one minute.  Add the remaining eggs, one at a time, beating for one minute between each addition.  Stop the bowl and scrape down the sides as necessary. Beat in vanilla extract.

Add half of the flour mixture to the egg and butter mixture.  Beat on low speed and slowly drizzle in the buttermilk.  Beat until just incorporated.  Stop the mixer, scrape down the bowl and add the rest of the dry ingredients.  Beat on low speed until just incorporated.  Remove the bowl from the stand mixer and finish incorporating with a spatula.  Try not to over mix the mixture.

Divide the batter between the prepared cupcake pans, filling each liner about two thirds full.  Bake for 18 to 20 minutes or until a cake tester inserted in the center of one of the cakes comes out clean.  Let rest in the cupcake pans before removing to a wire rack to cool completely.  Cupcakes should be completely cooled before frosting.

To make the frosting:

Place cream cheese in the bowl of an electric stand mixer.  Beat on medium speed for about 30 seconds, until very soft and pliable.  Stop the mixer, scrape down the sides of the bowl and add the butter and dulce de leche.  Beat on medium speed until well incorporated.  Stop the mixer and add the salt and powdered sugar.  Beat on medium speed for about 3 minutes, until fluffy and lighter in color.  Generously spoon frosting on top of cupcakes, or use a large frosting tip to pipe on frosting.

For garnish, I heated a few spoonfuls of dulce de leche of a low flame until just pourable.  Then I drizzled it over the cupcakes and topped with a few sprinkles.  Add a few sprinkles of fine sea salt if you’re feeling fancy.  I stored the cupcakes in the fridge for an hour to chill the frosting slightly.

I like to enjoy my cupcakes within two days of preparing them.  Feel free to wrap and refrigerate them because of the cream cheese in the frosting.  Let come close to room temperature before serving.