In a bowl, whisk together the milk, water, and flour until smooth and lump-free.
In a separate bowl, whisk the eggs with the melted and cooled butter, then pour this mixture into the milk–flour mixture and whisk until smooth; alternatively, combine all ingredients in a blender and puree until smooth.
Let the batter rest at room temperature for 15 minutes; it should have the consistency of heavy cream.
Heat a 10-inch nonstick skillet or crepe pan over medium heat and lightly brush or wipe with vegetable oil or melted butter.
Pour about 1/4 cup of batter into the hot pan and immediately swirl to coat the bottom in a thin, even layer (about 10 inches diameter and 1/16-inch thick).
Cook until the underside is lightly browned, about 2–3 minutes, loosen the edges with a thin spatula, flip, and cook the second side until light golden spots appear, about 30–60 seconds more.
Stack finished crepes on a plate and repeat with remaining batter, re-greasing the pan as needed.
Spread 1–2 tablespoons Nutella on each crepe, add fresh fruit as desired, and fold in half or into quarters to serve.