Preheat oven to 350°F (175°C). Line an 8×8-inch square baking pan with parchment paper, leaving an overhang on two sides for easy removal later. This prevents sticking and makes lifting the bars out simple.

In a large bowl, whisk together the flour, granulated sugar, brown sugar, and salt until well combined.

Pour in the melted butter and vanilla extract. Stir with a spatula until the mixture is evenly moistened and clumps together when pressed between your fingers.

Reserve half of the dough about 1 ½ cups (325g) of this mixture for the crumble topping and set aside.

Press the remaining dough firmly and evenly into the bottom of your prepared pan to form the crust.

In a medium bowl, combine strawberries, lemon juice + zest, cornstarch, sugar, vanilla, and salt.

Gently stir until the berries are evenly coated and the cornstarch has dissolved. The lemon juice will help the fruit release its juices, creating a naturally jammy texture while baking. Don't pour all the juices onto the bars, you can discard it.

Spread the strawberry filling evenly over the crust.

Sprinkle the reserved crumble mixture evenly over the top, leaving some berries peeking through for a rustic look.

Bake for 40–45 minutes, or until the topping is golden brown and the strawberry filling is bubbling around the edges.

Allow the bars to cool completely in the pan — at least 1–2 hours. This helps the filling set so the bars slice cleanly. Use the parchment overhang to lift the bars out, then cut into squares or rectangles.