Preheat the oven to 350°F (175°C) and lightly grease a 12-cup muffin tin.
In a blender or bowl, combine the melted butter, sugar, eggs, milk, flour, lemon juice, lemon zest, vanilla extract, and salt. Blend or whisk until smooth.
Pour the mixture evenly into the muffin cups, filling each about two-thirds full.
Bake for 28–32 minutes until the tops are lightly golden and centers are just set.
Cool in the tin for 10 minutes, then transfer to a wire rack. Chill for at least 1 hour before serving.
