Combine all ingredients except butter in the carafe of a blender and blend thoroughly. Allow to stand for thirty minutes in the refrigerator.
Melt half the butter in an eight-inch diameter skillet, preferably a non-stick skillet (see note). Pour in enough batter just to coat the bottom of the skillet and swirl pan until it is evenly distributed.
Cook over medium-low heat until the top is set and the bottom is golden when lifted gently with a spatula. Do not turn wrappers! Transfer wrappers to paper towels in one layer, golden side down. Repeat until all batter is used.
If no non-stick skillet is available, more butter will be required.
In a food processor, process the cheeses and sugar until smooth. If too liquidy, add the flour to thicken.
Put three tablespoons of the filling in the center of each wrapper, keeping the golden side down for the exterior, and fold the opposite sides of the wrapper over the filling. Fold in the ends to completely enclose the filling, forming packets, and arrange these packets, seam sides down, on the baking sheet.
When all wrappers are filled and have been transferred to the baking sheet, cover the sheet loosely with aluminum foil. Bake blintzes until heated through, about seven to 10 minutes.
Preheat oven to 250°F; line a baking sheet with Gefen Parchment Paper (preferred) or use a non-stick baking sheet.
Serve with sour cream and sugar as toppings, and with assorted fruit jams (optional).