It's important to have all ingredients for the crepes at room temperature before mixing to avoid clumps in the batter. Whisk together the eggs, butter, sugar and milk in a large mixing bowl for a few minutes, until smooth. Gradually add the flour, whisking well after each addition. Whisk until no clumps remain!

Preheat an 8-inch non-stick crepe pan or frying pan over medium heat. Add about 1/4 cup of batter at a time to the pan, tilting the batter around the pan to form a crepe. Cook the crepe on the first side for 1 minute, then turn the crepe once sides start turning golden brown. Cook on the second side for 30 seconds, then remove and stack onto a plate.

Preheat the oven to 350F. Next, prepare the filling. Place the cheese, egg, sugar and optional vanilla into a large mixing bowl. Use a large spoon to mix everything together, until a uniform filling forms. If desired, add 1/3 cup raisins or dried cranberries to the filling.

For each nalesnik: place a generous amount of the filling (about 2 tablespoons) into the center of each crepe. Fold each crepe as you would an egg roll: sides folded in first, then roll from top. Alternatively, spread the filling evenly to the edges and roll the crepes into a log. Place the nalesniki seam side down into large glass baking dish or casserole pan.

Add the cubed butter on top of the crepes and cover the pan with foil. Bake the cheese crepes for 30 minutes; bake the first 20 minutes covered with foil and the last 10 minutes without the foil.

Let the cheese crepes cool slightly before serving with fruit and/or whipped cream.