Use an electric mixer to blend together all the crêpe ingredients (except the butter for the pan) in a large bowl. Blend just until smooth. The batter will be very thin.
Combine the filling ingredients in a medium bowl and mix by hand. Keep the filling nearby.
Preheat a 10-inch frying pan over medium heat. (This size pan tapers to about 8 inches at the bottom.) When the pan is hot, add about ½ teaspoon butter.
When the butter has melted, pour 1/3 cup batter into the pan. Swirl the batter so that it entirely coats the bottom of the pan. Cook for 1½ to 2 minutes or until golden brown on one side.
Use a spatula to lift an edge of the crêpe. Grab it with your finger, slip the spatula underneath, and quickly flip it over. Cook for another 1½ minutes or until a bit lighter shade of brown than the first side, and then slide it out of the pan. Repeat with the rest of the batter and stack the finished crepes on top of each other to keep them warm.
Heat the cheese filling in the microwave for 1 to 2 minutes or until hot. When ready to fill the crêpes, place each crepe, dark side down, on a plate. Pour 2 to 3 Tablespoons of cheese filling across the center of the crêpe. Fold the sides in and turn the entire blintz over (to hide the seam) onto a serving plate.
Serve 2 to 3 blintzes on each plate with one dollop of sour cream and two of strawberry preserves. Sprinkle with powdered sugar.