Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment, leaving overhang for easy lifting.

Make the crust: In a bowl whisk the flour, granulated sugar, and salt. Cut in the cold cubed butter with a pastry cutter or two forks until the mixture resembles coarse crumbs and holds when pressed.

Press the crumb mixture firmly and evenly into the prepared pan. Bake 15–18 minutes, until lightly golden at the edges.

Optional lavender infusion: Warm the lemon juice slightly and stir in the dried culinary lavender. Steep 5 minutes, then strain well through a fine-mesh sieve. (Alternatively, grind the lavender very finely and use it directly in the filling for a stronger floral note.)

Make the filling: In a medium bowl whisk the eggs until smooth. Whisk in the granulated sugar until slightly thickened and pale. Add the lemon juice (infused or plain), lemon zest, flour, and baking powder; whisk until smooth.

Pour the filling over the hot crust and return the pan to the oven. Bake 20–25 minutes, until the edges are set and the center is just set with a slight jiggle.

Cool completely in the pan, then refrigerate at least 1 hour for clean slices.

Lift out using the parchment, dust generously with powdered sugar, slice into bars, and serve chilled or at room temperature.