Go ahead and preheat the oven to 350°F. While it's warming up, lightly grease a 9x13-inch baking dish.
Take the lemon curd (or pie filling) and pour it into the baking dish. Make sure that you spread it nice and even across the bottom.
Take the softened cream cheese, egg, and granulated sugar and then put them into a mixing bowl. Whip everything together until it's nice and creamy. After you've got everything nicely mixed, drop spoonfuls of it over the top of the lemon curd/pudding layer. Do your best to spread it out evenly.
Begin sprinkling the lemon cake mix over the creamy layer. Once you're done, slice the cold butter thin and place them in a single layer over the top.
Put the baking dish in the oven and bake it for about 40-45 minutes. What you want to see is a golden-brown crust with bubbling around the edges. Once you've got that, it's done!
Remove it from the oven and allow it to rest for about 15 minutes. For an extra delicious treat, add a scoop of vanilla ice cream or a nice dollop of whipped cream.