Preheat oven to 350°F. Line an 8x8 baking pan with parchment, leaving overhang on all four sides.

In a large bowl or stand mixer, beat together butter and sugars until light and fluffy. Mix in eggs, one at a time. Scrape bowl as needed. Mix in salt and baking powder, followed by lemon zest. Add lemon curd one tablespoon at a time, mixing until just combined. Lastly, mix in flour, increasing speed and mixing until fully combined and no streaks remain.

Press batter into prepared pan, creating an even layer. Lightly grease hands if needed to prevent sticking.

Bake for 30 minutes or until edges are just golden. Cool in pan on a wire rack. Remove bars by grabbing the parchment paper, pulling up and outwards. Using a sharp knife, cut into 9 equal pieces. Store in an airtight container.