Preheat oven to 350°F (175°C). Line a 9×13-inch baking dish with parchment paper.
In a large bowl, combine the sugar cookie mix, butter, and salt. Mix with a fork until crumbly.
Set aside ½ cup of the crumb mixture for topping.
Press the remaining mixture evenly into the bottom of the prepared baking dish.
In a medium bowl, use a hand mixer to beat the cream cheese and sugar until smooth.
Add the flour, lemonade concentrate, vanilla, pudding mix, and egg. Mix until just combined. Do not overmix.
Drop spoonfuls of the lemonade filling over the crust and gently spread to the edges, being careful not to disturb the crust.
Sprinkle the reserved ½ cup cookie crumble evenly over the top.
Bake for 30–35 minutes, or until the edges are lightly golden and the center is just set.
Let cool in the pan for 1 hour. Then, refrigerate for at least 3 hours (or overnight) to fully set.
Slice and serve chilled. Top with whipped cream, if desired.
