Prepare the Oven and Ramekins:
Preheat the oven to 425°F (220°C). Grease and flour 2 to 4 ramekins (depending on size) and set aside.

Mix the Batter:
In a large bowl, whisk together the egg, egg yolks, and vanilla extract until the mixture is creamy and pale. Add the dulce de leche and salt, continuing to whisk until smooth. Carefully fold in the flour, mixing gently to avoid overworking the batter.

Fill the Ramekins:
Pour the batter into the prepared ramekins, leaving a little space at the top for the cakes to rise.

Bake the Cakes:
Bake in the preheated oven for about 15 minutes, or until the edges are set but the center is still jiggly. Remove from the oven and allow the cakes to cool for about 1 minute.

Serve:
Run a sharp knife around the edges of the cakes and carefully flip them onto individual plates. Garnish with powdered sugar and fresh berries, if desired, and serve.