Preheat the oven to 350 degrees F (175 degrees C). Butter a 6-cup muffin tin. Line the bottoms with parchment paper cut into circles.

Mix graham cracker crumbs, butter, and sugar together in a small bowl. Distribute mixture evenly into the muffin cups and press firmly to form the crusts.

Bake in the preheated oven for 5 minutes. Leave oven on and let crusts cool for 5 minutes.

Meanwhile, beat cream cheese, sugar, egg, lemon juice, milk, flour, and vanilla extract together in a medium bowl until light and fluffy. Mix in egg; pour batter into the prepared muffin cups.

Bake in the preheated oven for 15 minutes.

Mix sour cream with sugar and vanilla extract in a small bowl. Top each cake with a small dollop of the mixture and continue baking until topping is set, about 10 minutes more.

Allow the cheesecakes to cool completely at room temperature before removing from the tin, at least 1 hour. Refrigerate.