Combine the milk, water, eggs, flour, salt and sugar in a blender. Blend on medium speed for 15 seconds, until the batter is smooth and lump-free. Scrape down the sides of the blender and pour in 3 tablespoons of melted butter. Blend it again for a second just to incorporate. Refrigerate the batter for 1 hour to let it rest. If the crepes are made immediately, they have a tendency to be rubbery; when you let the batter rest, the crepes have a better texture and a softer bite.
Put an 8-inch crepe pan or nonstick skillet over medium heat and brush with a little melted butter for added assurance. Pour 1/4 cup of batter into the pan and swirl it around so it covers the bottom evenly; pour back any excess. Cook for 30 to 45 seconds, until the crepe batter sets. Lightly bang the edge of the pan with a wooden spoon to loosen the crepe; then flip it and cook another 30 seconds. The art of flipping a crepe in the air takes practice, so make sure no one is looking when you get the first one going. If this intimidates you, use a heatproof rubber spatula to loosen and flip the crepe. The crepes should be pliable, not crisp, and lightly brown. Slide them onto a platter and continue making the crepes until all the batter is used. Cover the stack of crepes with a towel to keep them from drying out. This makes 10 crepes.
Assembly: Preheat the oven to 400 degrees F. Forming the blintzes is kind of like making burritos. Spoon 1/4 cup of the Cheese Filling along the lower third of the crepe. Fold the bottom edge away from you to just cover the filling; then fold the 2 sides in to the center. Roll the crepe away from you a couple of times to make a package, ending with the seam side down. Put an ovenproof skillet over medium heat. Brush with melted butter. Pan-fry the blintzes for 2 minutes per side until crisp and golden.
Transfer the pan to the oven and bake for 10 minutes so the egg in the filling cooks slightly and the cheese sets. Using a spatula, transfer the blintzes to serving plates. Spoon the Blueberry Sauce on top, dust with confectioners' sugar, and serve right away.
Serve with chopped banana and remaining Blueberry Sauce. Sprinkle with powdered sugar and serve.
In a food processor, combine the ricotta cheese, cream cheese, confectioners' sugar, lemon zest, and egg and blend until smooth. Chill the filling to firm it up a bit so it doesn't squirt out of the blintzes.
Combine the butter, blueberries, sugar, cornstarch, and lemon juice in a small pot over medium-high heat. Bring up to a low boil and stir gently until the berries break down and release their natural juices. The consistency should remain a bit chunky. It will thicken up when it cools down slightly.