1. Prepare the Crepe Batter: In a large bowl, whisk together the active sourdough starter, all-purpose flour, eggs, milk, 2 tablespoons granulated sugar, and salt until smooth. Make sure there are no lumps of flour. Stir in the 2 tablespoons of melted butter. The batter should be thin, similar to heavy cream. If it seems too thick, add a tablespoon or two more milk.

2. Rest the Batter (Optional but Recommended): For best results, cover the bowl with plastic wrap and let the batter rest in the refrigerator for at least 30 minutes, or even overnight. This allows the flour to fully hydrate and the gluten to relax, resulting in more tender crepes. If you’re short on time, you can proceed directly to cooking.

3. Make the Cheese Filling: While the batter rests, prepare the blintz filling. In a medium bowl, beat the softened cream cheese with 1/4 cup granulated sugar and vanilla extract until smooth and creamy. If using, stir in the lemon zest. Set aside.

4. Heat the Skillet: Heat a non-stick skillet or crepe pan (8-10 inches) over medium heat. Lightly brush the pan with a small amount of melted butter or oil. A well-seasoned cast iron skillet also works wonderfully. The pan is ready when a drop of water sizzles instantly.

5. Cook the Crepes: Pour about 1/4 cup of batter into the hot skillet. Immediately tilt and swirl the pan to evenly coat the bottom with a thin layer of batter. Cook for 1-2 minutes, or until the edges begin to crisp and the surface appears set and dry. The underside should be lightly golden brown.

6. Flip and Finish Crepes: Gently loosen the edges with a spatula, then carefully flip the crepe. Cook for another 30-60 seconds on the second side, just until lightly browned. Slide the cooked crepe onto a plate. Repeat with the remaining batter, stacking the cooked crepes as you go. You may need to lightly grease the pan between crepes.

7. Assemble the Blintzes: Lay a crepe flat on a clean surface. Place about 2 tablespoons of the cheese filling near one edge of the crepe. Fold the short sides of the crepe over the filling, then roll it up tightly from the filled edge, creating a neat blintz. Repeat with all crepes and filling.

8. Serve Warm: You can serve the blintzes immediately, or lightly pan-fry them in a little butter for a minute or two per side until golden and warmed through. This step adds a lovely crispiness.