Preheat your oven to 350°F (175°C) and prepare a 9x9-inch baking pan by greasing it and lining it with parchment paper.

In a mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until well combined.

In a separate bowl, beat the softened unsalted butter and large eggs until smooth, then combine with the dry ingredients until just incorporated.

Spread the batter evenly in the prepared baking pan and gently tap to remove air bubbles.

In another bowl, whisk together the granulated sugar, cornstarch, fresh orange juice, orange zest, large eggs, and vanilla extract until smooth, then pour over the crust.

Bake for 25 to 35 minutes until the edges are set and a toothpick comes out mostly clean.

Let the bars cool completely in the pan on a wire rack before preparing the glaze.

Mix powdered sugar with fresh orange juice and zest until smooth, then drizzle over the cooled bars and cut into squares.