Preheat your oven to 350°F and line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.

In a large bowl, whisk together the flour, granulated sugar, packed brown sugar, and salt.

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

Reserve 1 cup of the crumb mixture for the topping and press the rest firmly into the bottom of the prepared pan to form the crust.

Bake this crust until the edges are lightly golden, about 15 minutes.

Meanwhile, in another bowl, toss the sliced strawberries with the granulated sugar, cornstarch, and lemon juice until evenly coated.

Remove the pan from the oven and spread the strawberry mixture evenly over the warm crust.

Sprinkle the reserved crumb mixture evenly over the strawberry layer.

Return the pan to the oven and bake until the topping is golden and the fruit filling is bubbly, around 25 minutes.

Allow the bars to cool completely in the pan, then refrigerate for at least 2 hours to set.

Once chilled, use the parchment overhang to lift the bars from the pan and cut into squares before serving.