Pre heat oven to 350°F with a rack in the center.
Line a baking sheet with parchment paper.
In medium bowl combine the butter and sugar and cream together with a handheld mixer for about 2 minutes.
Add the egg whites and vanilla extract and mix until combined.
Add the flour, cornstarch and salt and mix on low until you achieve a pancake batter consistency.
Add a tablespoon of the batter to the prepared baking sheet and with the back of the spoon spread the batter in a circular motion to create a thin disk. Add to 3-4 disk at a time
Bake for 5-6 minutes until the edges start browning. With a spatula lift the edge of the disk and with chopstick start rolling it to create a cilynder-like shape.
Place them on a cooling rack and repeat with the rest of the batter.
Fill a pastry bag with ¼ cup dulce de leche and fill the barquillos.
Dip them in melted chocolate and cover with sprinkles.