Preheat oven to 350°F (175°C). Grease a 12-cup muffin tin thoroughly.
In a blender or large bowl, combine milk, eggs, melted butter, and vanilla extract. Blend until smooth.
Add the sugar and biscuit baking mix. Blend for another 60 seconds until a thin batter forms.
Gently fold in the fresh lemon juice and lemon zest by hand.
Pour batter into muffin cups, filling 3/4 full. Bake for 20-25 minutes until centers are set and tops are golden.
Cool completely in the pan, then refrigerate for at least 1 hour before carefully unmolding.
