Preheat the oven to 325°F. Line 20 muffin cups with paper liners.

In a medium bowl, combine the cracker crumbs and butter. Divide the mixture between the liners and press firmly into the bottoms. Bake for 10 minutes, until dry in the center. Reduce the oven temperature to 300°F.

In a large bowl, beat the cream cheese with an electric mixer, until smooth. Add the sugar, sour cream or yogurt, eggs, lemon juice, vanilla, and salt and beat on medium-high for 2 to 3 minutes, until smooth, scraping down the sides as needed.

Divide the mixture evenly between the muffin cups. (They should be almost full.)

Bake for 20 to 22 minutes, or until the centers are nearly set.

Remove from the oven and let cool in the pan for 20 to 30 minutes before removing to a wire rack to cool completely.

Refrigerate for at least 3 to 4 hours, until chilled before serving as desired.