Preheat the oven to 350°F (175°C). Grease the baking pan.

In a mixing bowl, cream together the softened butter and sugar until light and fluffy.

Add flour and salt, mixing until just combined. Press the mixture into the bottom of the prepared pan.

Bake for 15-20 minutes or until lightly golden.

In another bowl, whisk together the sugar, eggs, lemon juice, lemon zest, flour, and baking powder until smooth.

Pour the filling over the baked crust and return to the oven.

Bake for an additional 20-25 minutes until set and slightly golden on top.

Allow to cool completely before cutting into squares.