To make the crepes: in a large bowl, food processor, or blender, mix the melted butter, eggs, milk, cold water, salt, and sugar. Add the flour a half cup at a time, mixing between each addition to remove as many lumps as possible.
In an 8” nonstick pan, melt a small pat of butter over medium heat. Pour about 1/3 cup of the batter into the center of the hot pan. Lift and rotate the pan immediately so batter coats the bottom entirely, then place the pan back on the heat to cook. You’ll get the hang of it after a couple of tries.
At first, each crepe will take about 1 minute, but the process speeds up as the pan gets hotter, and each crepe should take 30 to 45 seconds. When the crepe is mostly cooked, the edges will lift up. With a spatula, check to make sure the crepe has splotches of brown on the bottom. When one side is fully cooked, flip the crepe onto a nearby plate lined with parchment paper so that the side that has not cooked is facing down.
Repeat with the remaining batter, stacking each crepe on top of the others. No need to butter between each crepe—only add more butter about every fifth crepe. Note that the first crepe never comes out well. Don’t despair.
To make the sweet cheese filling: combine all the ingredients in a bowl and mix well.
To form the blintzes: spoon about 1/4 cup of the filling onto the cooked side of a crepe, in the middle of the lower half. Spread out the filling from side to side in a horizontal line. Fold the bottom of the crepe up to cover the filling from side to side in a horizontal line. Fold the bottom of the crepe up to cover the filling, and then fold each end into the center to create a small package.
Roll up the crepe tightly to form a compact blintz. It will be about 4 inches in length. Repeat with the remaining crepes and filling.
At this point, you can fry them up to eat immediately or refrigerate or freeze them to eat later. To refrigerate, wrap each blintz individually in parchment paper (so they don’t stick together) and store in an airtight plastic container for up to 5 days. To freeze, set the wrapped blintzes on a baking sheet in the freezer until they harden, then transfer to an airtight plastic container and freeze for up to 3 months.
If you prepared your blintzes in advance, be sure to bring them up to room temperature before frying them (so the filling doesn’t remain cold). Place a small pat of butter in a nonstick skillet over medium-low heat and place the blintzes in the pan, seam side down. If your blintz is cylindrical, flatten it slightly with a spatula for even cooking. Do not crowd the pan. Cook the blintzes until golden on the bottom, then flip to the other side and cook until golden brown and the sides are soft, 3 to 4 minutes total. You may need to flip each blintz multiple times to avoid them getting too brown.