Heat the oven to 350°F. Thoroughly coat a 24-cup mini muffin pan with nonstick baking spray, paying attention to the sides and corners of each cavity.

Divide the refrigerated sugar-cookie dough into 24 portions, approximately 2 teaspoons each. Roll each portion into a ball and place one ball in each prepared mini muffin cup.

Bake for 10-12 minutes, or until the edges are lightly golden while the centers still look soft. Do not wait for the centers to become deeply browned, since the cookies will continue to set as they cool.

Immediately press down the center of each warm cookie with the back of a small measuring spoon or a tart tamper. Make shallow, even cups while the dough is still warm and flexible.

Cool the cookie cups in the pan for about 10 minutes. Transfer them carefully to a wire rack and cool completely before adding the filling.

Whisk the sweetened condensed milk and thawed lemonade concentrate together in a bowl until smooth. Add the lemon zest if using, then gently fold in the thawed whipped topping without overmixing.

Spoon or pipe approximately 1 tablespoon of lemonade filling into each cooled cookie cup. Refrigerate the filled bites for at least 1 hour, or for 2 hours if you prefer a firmer filling.

Garnish with small lemon slices or extra lemon zest just before serving. Keep the bites chilled until they are ready to be placed on a dessert platter.