Preheat oven to 350°F (175°C). Grease a 9-inch pie pan with butter.
In a large bowl, whisk eggs and sugar until pale, about 30 seconds.
Add milk, lemon juice, zest, melted butter, and salt; whisk until silky smooth.
Pour mixture into the prepared pan. Bake on the center rack 35–40 minutes until golden edges form and the center jiggles slightly.
Cool on a wire rack 15 minutes, then refrigerate at least 2 hours until set.
Notes
For best results, bring eggs and milk to room temperature to ensure even baking.Use fresh lemon juice and fully dissolve sugar to create a smooth texture and prevent graininess.