Preheat your oven to 350°F (175°C). Line a 9-inch baking pan with parchment paper, leaving an overhang for easy removal.
In a mixing bowl, combine 1 1/2 cups of flour, 1/2 cup of granulated sugar, and add the cold, diced butter. Use a pastry cutter or your fingers to blend until the mixture resembles coarse crumbs with pea-sized clusters.
1 1/2 cups all-purpose flour, 1/2 cup granulated sugar, 1/2 cup unsalted butter
Press the crumb mixture evenly into the prepared baking pan to form a compact crust. Bake in the preheated oven for 15-18 minutes, or until lightly golden around the edges.
While the crust bakes, prepare the strawberry filling: In a bowl, toss the sliced strawberries with 2 tablespoons of sugar and the lemon zest. Add lemon juice if using. Let sit for 10 minutes so the flavors meld and juices release.
1 cup fresh strawberries, 2 tablespoons granulated sugar, 1 tablespoon lemon zest, 2 tablespoons fresh lemon juice
Once the crust is baked and slightly cooled, evenly distribute the strawberry mixture over the crust. Pour the remaining juice from the strawberries over the top to soak into the crust slightly.
Create the streusel topping by mixing 1 cup of flour, 1/2 cup of sugar, and enough melted butter to form clumps. Sprinkle the topping evenly over the strawberries.
1 1/2 cups all-purpose flour, 1/2 cup granulated sugar, 1/2 cup unsalted butter
Return the assembled bars to the oven and bake for an additional 20-22 minutes, until the topping is golden brown and the filling is bubbling.
Remove from the oven and let cool in the pan for at least 30 minutes. Use the parchment overhang to lift the bars out onto a wire rack. Slice into squares and serve.
