In a mixing bowl, combine ricotta cheese, cream cheese, sugar, vanilla extract, and egg. Mix until smooth.

In another bowl, whisk together flour, milk, eggs, melted butter, and salt until smooth.

Heat a frying pan over medium heat and pour in a small amount of batter, swirling to coat the pan. Cook until edges are set, then flip and cook the other side.

Place a crepe on a plate, add a spoonful of filling, and fold the crepe over the filling. Repeat with remaining crepes and filling.

In the same frying pan, add a little butter and cook the filled blintzes until golden brown on both sides.