Step 1: Make the Crepes

1. In a mixing bowl, whisk together the flour, sugar, and salt.
2. In a separate bowl, beat the eggs and milk until combined. Gradually add the wet ingredients to the dry ingredients, whisking until smooth. Stir in the melted butter.
3. Heat a non-stick skillet or crepe pan over medium heat and lightly grease with butter. Pour about 1/4 cup of batter into the pan, swirling to coat the surface evenly.
4. Cook for 1-2 minutes, or until the edges lift easily and the crepe is lightly golden. Flip and cook for an additional 30 seconds. Transfer the crepe to a plate and repeat with the remaining batter, stacking the crepes with parchment paper in between to prevent sticking.

Step 2: Prepare the Cheese Filling

1. In a medium bowl, combine the ricotta, cream cheese, powdered sugar, vanilla extract, and lemon zest. Mix until smooth and creamy. Set aside.

Step 3: Make the Raspberry Sauce

1. In a small saucepan, combine the raspberries, sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the raspberries break down and the mixture begins to bubble, about 5 minutes.
2. For a thicker sauce, stir in the cornstarch slurry and cook for another 1-2 minutes until slightly thickened. Remove from heat and let cool.

Step 4: Assemble the Blintzes

1. Place a crepe on a flat surface and spoon about 2 tablespoons of the cheese filling onto the lower third of the crepe. Fold the bottom edge over the filling, then fold in the sides and roll tightly into a neat package. Repeat with the remaining crepes and filling.

Step 5: Cook the Blintzes

1. Heat a large skillet over medium heat and add a tablespoon of butter. Place the filled blintzes seam-side down in the skillet and cook for 2-3 minutes on each side, or until golden brown and slightly crisp.
2. Remove from the skillet and keep warm.

Step 6: Serve

1. Arrange the blintzes on a plate, drizzle generously with the raspberry sauce, and garnish with fresh raspberries or a sprinkle of powdered sugar. Serve immediately.