Prepare the Cookie Base:

Preheat Oven: Preheat your oven to 350°F (175°C). Grease and line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.

Mix the Cookie Base: In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. Gradually add the flour, salt, and baking powder, mixing until a dough forms.

Press into Pan: Press the cookie dough evenly into the bottom of the prepared baking pan. Bake for 15-18 minutes, or until lightly golden.

Prepare the Lemon Filling:

Mix the Lemon Filling: In a separate bowl, whisk together the eggs, granulated sugar, flour, baking powder, lemon zest, and lemon juice until well combined.

Pour Over Cookie Base: Once the cookie base is done baking, remove it from the oven and pour the lemon filling over the hot base.

Bake Again: Return the pan to the oven and bake for an additional 15-20 minutes, or until the lemon filling is set and the edges are lightly golden.

Cool and Serve:

Cool: Remove from the oven and allow to cool in the pan for about 30 minutes. Then transfer to the refrigerator to chill for at least another 30 minutes before cutting.

Slice and Dust: Once chilled, use the parchment overhang to lift the bars out of the pan. Dust with powdered sugar if desired and cut into squares or bars.