Preheat your oven to 350°F (175°C). Grease a 9x9-inch baking pan and set it aside.

In a large mixing bowl, combine the lemon cake mix, melted butter, and 1 egg. Mix well until the ingredients are fully combined and a thick dough forms.

Take about two-thirds of the dough and press it evenly into the bottom of the greased baking pan to form the base layer.

In a separate bowl, mix together the marshmallow fluff, lemon juice, and remaining egg. Stir until well combined and smooth.

Pour the marshmallow mixture over the dough in the baking pan. Use a spatula to spread it out evenly.

Crumble the remaining one-third of the dough over the top of the marshmallow layer, creating a crumbly topping.

Place the pan in the preheated oven and bake for 25-30 minutes or until the edges are golden brown and the center is set.

Remove from the oven and allow the lemon bars to cool completely in the pan.

Once cooled, dust the top with powdered sugar, if desired, for an extra touch of sweetness.

Cut the lemon bars into squares or rectangles and serve. They can be stored in an airtight container at room temperature for up to 3 days.