Preheat oven to 350°F (175°C). Lightly grease a 12-cup muffin tin or line with cupcake liners.
In a mixing bowl, whisk together the melted butter, sugar, and flour until well combined.
Add eggs one at a time, whisking well after each addition.
Pour in the milk, lemon juice, lemon zest, vanilla extract, and salt. Mix until smooth.
Divide the batter evenly among the muffin cups, filling about ¾ of the way.
Bake for 22-25 minutes or until the pies are set and slightly golden on top.
Let the pies cool in the pan for 10 minutes before transferring them to a wire rack to cool completely.
Dust with powdered sugar before serving.