1. Prepare the Crust and Topping:

1.Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish or line it with parchment paper for easy removal.

2.In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.

3.Add the cold, cubed butter and vanilla extract to the dry ingredients. Use a pastry cutter or your fingers to mix until the texture resembles coarse crumbs.

4.For added texture, stir in the oats (optional).

5.Press two-thirds of the crumb mixture into the bottom of the prepared baking dish, reserving the remaining third for the topping.

6.Bake the crust in the preheated oven for 15–20 minutes, or until it turns light golden brown. Remove from the oven and let it cool slightly.

2. Prepare the Lemon Filling:

1.In a large bowl, whisk the eggs until well combined.

2.Gradually add the sugar and flour, whisking until smooth and lump-free.

3.Pour in the lemon juice and add the lemon zest. Stir until the mixture is fully blended.

3. Assemble and Bake:

1.Pour the lemon filling evenly over the slightly cooled crust.

2.Sprinkle the reserved crumb mixture evenly over the top of the filling.

3.Return the baking dish to the oven and bake for an additional 20–25 minutes, or until the filling is set and the crumb topping is golden.

4. Cool and Serve:

1.Let the bars cool completely in the pan. For best results, chill them in the refrigerator for 1–2 hours before slicing.

2.Dust with powdered sugar before serving. Add fresh berries or coconut flakes for garnish, if desired.