For the blintzes, combine the flour, eggs, milk, and salt in an electric blender and process until smooth.
Refrigerate for 1 hour.
Melt a small amount of butter in a crepe pan or 8-inch (20 cm) non-stick skillet over moderate heat.
Pour in just enough batter to coat the bottom of the pan and cook on both sides until light golden brown.
Turn onto a plate and repeat to make the remaining blintzes.
Combine the filling ingredients and stir to mix thoroughly.
Place a spoonful on each blintz, fold the ends towards the center and roll up.
Melt a little butter in a saute pan and saute the blintzes until golden on both sides.
Garnish with reserved blueberries and powdered sugar if desired.