Preheat your oven to 175°C (350°F). Line your baking pan with parchment paper, leaving some overhang so you can easily lift the bars later.

In a large bowl, mix flour, oats, brown sugar, baking powder, and salt. Pour in melted butter and vanilla extract. Stir until the mixture becomes crumbly but slightly moist.

This mixture will serve as both the base and the topping.

Take about two-thirds of the crumble mixture and press it firmly into the bottom of your prepared pan. Make sure it’s even and compact so it holds together after baking.

In another bowl, whisk eggs and sugar until smooth. Add lemon juice, lemon zest, flour, and salt. Whisk again until everything is fully combined and slightly thickened.

This filling should smell bright and fresh—that’s when you know it’s right.

Pour the lemon filling over the pressed crust. Spread evenly using a spatula.

Then sprinkle the remaining crumble mixture over the top. Don’t press it down—you want a loose, crumbly texture.

Bake for 30–35 minutes or until the top is golden and the lemon filling is set.

You’ll know it’s ready when the edges look slightly golden and the center is no longer jiggly.

This step is important. Let the bars cool in the pan for at least 1 hour. Then lift them out using the parchment paper and slice into squares.