Preheat oven to 350F.

Prepare the crust by beating the softened butter, cream cheese, and 1/2 cup granulated sugar together with an electric mixer until light and fluffy.

Beat in the egg yolk.

Gradually add 3/4 cup flour and mix until combined.

Spread the dough into a greased 8-inch square baking dish.

Sprinkle 2 tablespoons of powdered sugar on top of the dough to prevent sticking while patting it down to form a crust.

Bake the crust for 20 minutes.

While the crust bakes, prepare the filling by slightly beating the egg and egg substitute in a mixing bowl.

Add 1 cup granulated sugar and 2 tablespoons flour to the egg mixture; beat on low speed until blended.

Add the lime juice to the filling mixture; beat on low speed until blended.

Pour the filling onto the warm shortbread crust.

Bake for an additional 15 minutes.

Place the baked lime bars on a rack to cool completely.

Sprinkle the top with 2 tablespoons or more of powdered sugar before serving.