Preheat your oven to 350°F (175°C). This ensures your bars bake evenly and become beautifully golden.
Line a 9x9 inch baking pan with parchment paper, leaving some overhang on the sides. This will make it easy to lift the bars out later for cutting.
In a mixing bowl, cream together the unsalted butter and powdered sugar until light and fluffy. This should take about 2-3 minutes. Add in 1 cup of all-purpose flour and a pinch of kosher salt, mixing until the dough comes together. Press the dough evenly into the bottom of the prepared pan.
Bake the crust in the preheated oven for about 15-20 minutes, or until it is lightly golden. Keep an eye on it, as you want it to achieve a nice golden color without burning.
While the crust is baking, you can prepare the filling. In a mixing bowl, whisk together the granulated sugar, 2 large eggs, 1 egg yolk, freshly squeezed Meyer lemon juice, finely grated lemon zest, vanilla bean paste, baking powder, and the 2 tablespoons of flour. Mix until everything is well combined and smooth.
Once the crust has finished baking, remove it from the oven and pour the lemon filling over the hot crust. This helps to set the filling nicely.
Return the pan to the oven and bake for an additional 20-25 minutes, or until the filling is set and has a slight jiggle in the center.
Once baked, remove the pan from the oven and let it cool on a wire rack. Once cooled to room temperature, transfer to the refrigerator to chill for at least 2 hours, allowing the bars to firm up.
Once chilled, lift the bars out of the pan using the parchment paper overhang. Cut into squares or rectangles and dust with sifted powdered sugar just before serving.
