1. In a blender, combine eggs, milk, water, flour, butter and salt. Process until smooth (if you don't have blender, you can whisk the ingredients). Cover and refrigerate for 1 hour, if you have the time.
2. Heat a skillet over medium-high heat and brush with oil. Pour 1/4 cup of batter, tilting the pan with a circular motion, so that the bottom surface gets coated evenly. When the bottom is light brown (after about a minute or less), loosen crepe with a spatula, flip and cook the other side. Place on a plate. Repeat with remaining batter.
3. To get perfect hard-boiled eggs, place them in a saucepan and cover with cold water. Make sure the tops of the eggs are covered by at least an inch of water. Bring the water to a full boil, cover and remove from the heat. Let stand for 15 minutes. Then place the eggs in a bowl of cold water. Finely chop or grate.
4. Warm a large skillet over medium-high heat. Add ground beef and onion, saute until the meat is lightly browned and fully cooked (no need to add oil). Use a spatula to break up the meat as it cooks, turn it occasionally to brown evenly. Season with salt and pepper. If your meat is high in fat content, you can drain some of the grease.
5. In a bowl, combine cooked ground beef and eggs. Add broth or mayonnaise to help the filling hold together, stir well.
6. Place a few spoonfuls of the filling in the center of each crepe (forming a log).
7. Fold the left and right edges toward the filling.
8. Bring the bottom side of the crepe over the filling.
9. Roll the crepe around the filling.
10. You can brown the crepes before serving (optional). Heat some butter in a large skillet and saute the crepes until nicely browned. Serve with sour cream. Cover and store unused crepes in refrigerator, or freeze.