Preheat oven to 350°F. Spray mini muffin pans with nonstick cooking spray (I use the kind with flour in it).
Cream butter and granulated sugar with a stand or a hand mixer until smooth and fluffy, about 1 minute. Mix in egg and vanilla then add baking soda, salt and cream of tartar and mix until smooth. Add flour and mix until cookie dough forms.
Scoop 1 tablespoon sized cookie dough balls and place each in one cavity of the muffin pan.
Bake for 18-20 minutes or until no longer glossy and a light golden around the edges.
Immediately upon removing the cookies from the oven, use the handle of a wooden spoon or the back of a teaspoon to press a cavity in the center and form the tart shell.
Let the cookies cool completely, then remove from the pan. The cookies should pop right out when nudged with a butter knife.
Fill each cookie with 1-2 teaspoons of lime curd. Sprinkle with lime zest for garnish.
Store in an airtight container in the refrigerator for up to 3 days. Cookies can be frozen without filling for up to 3 months.