To make the blintz batter, in a bowl, whisk together the flour and salt. Add the eggs, milk, and ¾ cup (6 fl oz/180 ml) water and whisk until smooth, then whisk in the 3 tablespoons melted butter. Cover and refrigerate for 1 hour. Alternatively, combine the initial ingredients in a food processor and process until smooth, about 4 seconds, then add the melted butter and process to mix. Pour into a bowl, cover, and refrigerate for 20 minutes.
To cook the blintzes, heat a large frying pan over medium heat until a drop of water flicked on the surface sizzles and evaporates. Brush with about ½ teaspoon room-temperature butter, then ladle ¼ cup (2 fl oz/60 ml) batter onto the center. Tilt the pan to cover the bottom evenly. Cook until the edges begin to brown and the top is set, 1½–2 minutes. Turn and cook for about 1 minute longer. Transfer to a plate. Repeat to make about 12 blintzes total, buttering the pan as needed and stacking the finished blintzes with waxed paper between them.
To make the cheese filling, in a bowl, stir together the cheeses, sugar, orange zest, and vanilla until well blended.
To assemble the blintzes, spread a generous 2½ tablespoons of the filling in the center of each blintz. Fold in the sides and then the ends to enclose the filling and form a rectangle. In a large frying pan over medium heat, melt 2 tablespoons of the butter. When the butter sizzles, add half of the blintzes, seam side down, and fry until lightly browned, about 2 minutes. Gently turn and fry the second side until lightly browned, about 2 minutes. Transfer to individual plates. Repeat with the remaining blintzes and butter. Serve hot with the compote.