Make the cheese filling by combining all the ingredients and mixing them until smooth. Put in the fridge while you prepare the batter.
To make the blueberry sauce, put all the ingredients in a saucepan and cook over medium heat until the blueberries start to burst. Simmer for a couple more minutes and set aside.
Prepare the crêpe batter: sift the flour, salt and sugar and set aside.
Whisk the eggs and slowly add the milk and melted butter, mixing until smooth.
Add the flour and whisk it in. Cover and set aside to rest for 10-15 minutes. The batter should have the consistency of pouring cream - if it's too thin add a little more flour - about 2 tablespoons.
Heat a teaspoon of butter in a non stick pan until just foaming. Pour some batter into the pan and swirl it around so it coats the whole bottom of the pan. Cook until bubbles form on top and the edges start to brown and curl. Put the crepe on a plate lined with kitchen towel.
Repeat until you use up all the batter adding extra butter on the pan if needed (I found that once was enough).
To make the blintze, take a crêpe, cooked side up, and place a tablespoon of filling near the edge closest to you.
Fold the bottom edge over to cover the filling, then fold the sides in. Roll the bottom of the blintz over and set aside. Repeat with rest of the pancakes.
Heat a teaspoon of butter in the pan. Once its foaming, place 4 blintzes, seam side down, on the pan and cook a couple a minutes on each side until golden.
Serve warm, drizzled with the blueberry sauce and dusted with icing sugar.