In a mixing bowl, whisk together the flour, milk, eggs, and salt until smooth. Let the batter rest for about 15 minutes.
Heat a non-stick skillet or crepe pan over medium heat and lightly coat with butter.
Pour a small amount of batter into the skillet, tilting to spread it evenly into a thin layer. Cook for about 1-2 minutes, or until the edges start to lift and the bottom is golden brown. Flip and cook for another 1-2 minutes on the other side.
Remove the pancake from the skillet and repeat with the remaining batter. Stack the cooked pancakes and let them cool.
Once cooled, roll up the pancakes tightly and slice them into thin strips to create the frittaten.
In a large pot, bring the beef broth to a boil. Add the sliced carrot and leek and reduce the heat to a simmer. Cook for about 10-15 minutes, or until the vegetables are tender.
Divide the frittaten (pancake strips) among serving bowls. Ladle the hot beef broth and vegetables over the frittaten.
Enjoy your meal!