Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.

In a mixing bowl, combine room-temperature cream cheese, melted butter, powdered sugar, and kosher salt. Beat until smooth and creamy, about 2-3 minutes.

Add the large egg to the cream cheese mixture and continue to mix for 1-2 minutes until fully incorporated.

Pour the cream cheese mixture into your greased baking dish and spread it evenly across the bottom.

Spoon lemon pie filling over the cream cheese layer, spreading it evenly without mixing.

Evenly sprinkle the cake mix over the lemon pie filling without stirring.

Drizzle melted butter over the sprinkled cake mix to enhance flavor and create a crispy top.

Bake in the preheated oven for 40-45 minutes until the top is golden brown and bubbling.

Allow to cool slightly before slicing into squares; serve warm with optional whipped cream or vanilla ice cream.