Preheat the oven to 350°F (180°C). Grease an 8x8 inch baking dish or line it with parchment paper for easy removal.
In a medium bowl, mix together the all-purpose flour and powdered sugar. Cut in the softened butter with a fork or pastry cutter until the mixture resembles coarse crumbs. Press this mixture firmly into the bottom of the prepared baking dish to form the crust.
Bake the crust in the preheated oven for about 15-20 minutes, or until lightly golden. Remove from oven and let it cool slightly while preparing the filling.
In a large mixing bowl, whisk together the Greek yogurt, granulated sugar, eggs, lemon zest, lemon juice, baking powder, and salt until smooth and well combined.
Pour the yogurt mixture over the pre-baked crust, spreading evenly.
Bake in the oven again for an additional 20-25 minutes, or until the filling is set and the edges are golden. A slight jiggle in the center is okay as it will firm up upon cooling.
Remove from oven and allow to cool completely at room temperature. Once cooled, refrigerate for at least 1 hour to set further.
Before serving, dust the top with powdered sugar for a lovely finish and cut into squares.
Notes
Serve chilled squares on a decorative plate, garnished with thin lemon slices or zest to enhance the citrus flair.