In a mixing bowl, whisk together flour, milk, eggs, sugar, and salt until smooth.

Heat a frying pan over medium heat and lightly grease it. Pour in a small amount of batter and swirl to coat the pan. Cook until the edges start to lift, then flip and cook for another minute.

In a bowl, mix together ricotta cheese, cream cheese, sugar, vanilla extract, and egg yolk until well combined.

Place a spoonful of cheese filling in the center of each crepe, fold the sides over, and roll up tightly.

In the same frying pan, cook the filled blintzes until golden brown on both sides.

Serve warm with sour cream, powdered sugar, and fresh berries on top.