Set your oven to 350°F (175°C) and generously grease a 12-cup muffin pan.
In a blender or a large mixing bowl, combine the milk, eggs, melted butter, and vanilla extract, blending until the mixture is smooth.
Add the sugar and biscuit baking mix to the liquid ingredients and blend for about a minute until the batter thins out.
Carefully mix in the fresh lemon juice and lemon zest using a spatula or spoon by hand.
Pour the batter into the prepared muffin cups, filling each about three-quarters full.
Bake in the preheated oven for 20 to 25 minutes until the centers have set and the tops turn golden brown.
Allow the pies to cool fully in the pan, then chill them in the refrigerator for at least one hour before gently removing from the tin.