1. In a large bowl, whisk together the flour, salt, and optional sugar if using.
2. In another bowl, beat the eggs then add the warmed milk, water, melted butter, and vanilla extract if desired.
3. Gradually pour the wet ingredients into the dry, whisking continuously until a smooth, slightly thick batter forms. Alternatively, blend all ingredients in a blender or food processor until smooth.
4. Cover and let the batter rest at room temperature for 30 minutes or refrigerate for up to two days. Resting helps develop a tender texture and easier spreading.
5. Heat a 10-inch (or 8-inch) nonstick skillet over medium heat and brush lightly with oil or butter.
6. Pour about 1/4 to 1/3 cup of batter into the skillet, immediately tilting and swirling it in a circular motion to form an even thin layer.
7. Cook for about 1 to 2 minutes until the edges start to lift and the bottom is lightly browned, then carefully flip and cook the other side for 30 seconds to 1 minute until golden. Adjust heat as needed to avoid burning.
8. Transfer cooked crepes to a plate and stack, covering with a clean towel to keep warm while cooking the rest. Add oil or butter between crepes as needed to prevent sticking.
9. Serve warm, filled or topped with sweet or savory fillings such as berries, syrup, nutella, cheese, sautéed vegetables, or meats. Crepes can be folded, rolled, or folded into triangles.