"I couldn't find any lime pie recipes with cream cheese, so I decided to create one. If you like light and fluffy tiny desserts, and dislike graham cracker crumb crusts, you'll love these! I used mini muffin pans, but I think this would be equally as good in a regular cheesecake pan."
Preheat oven to 425 degrees F (220 degrees C). Grease a 12-cup muffin tin with cooking spray.
Melt butter in a saucepan over medium-low heat, about 3 minutes.
Place vanilla wafers in a food processor; blend until crumbly but not powdery. Pour into a bowl; add the melted butter, 1/2 cup sugar, and butter flavoring. Mix with a fork; let set until crumbs soften, about 2 minutes. Tightly pack pinches of the crumb mixture over the bottoms of the muffin cups.
Bake in the preheated oven until starting to brown, about 4 minutes. Reduce oven temperature to 325 degrees F (163 degrees C). Let crusts cool.
Mix cream cheese, condensed milk, and egg yolks together in a bowl using a fork until smooth. Let set, about 1 minute. Juice 2 limes into the mixture. Peel the green rind off the third lime; zest the white rind into the mixture. Juice the lime into the mixture. Mix until smooth.
Whip the egg whites in a bowl using clean beaters until foamy. Gradually add 1/4 cup sugar and cream of tartar, continuing to beat until stiff peaks form. Fold cream cheese-lime mixture into the whipped egg whites gently with a flat spatula until thoroughly blended. Spoon into the crusts; fill muffin cups to the rim.
Bake in the hot oven until edges start to brown, 13 to 14 minutes. Let cool, at least 15 minutes.