Preheat your oven to 350°F (175°C) and line your baking pan with parchment paper, leaving overhang for easy removal.
In a large bowl, whisk together the flour and granulated sugar for the crust. Add the cold, cubed butter and use a pastry cutter or your fingers to work it in until the mixture resembles coarse crumbs.
Add the egg and vanilla extract to the crumb mixture and stir with a spatula until just combined. This dough should hold together when pressed.
Press about two-thirds of the crumb mixture into the bottom of the prepared baking pan, spreading evenly and pressing firmly to create an even crust layer.
In a separate bowl, combine the sliced strawberries, lemon juice, lemon zest, sugar, and cornstarch. Toss gently to coat all the berries evenly.
Spread the strawberry filling evenly over the crust layer in the pan.
Crumble the remaining biscuit mixture evenly over the berry filling, ensuring some of the filling peeks through for a beautiful, layered look.
Bake in the preheated oven for about 35 minutes, or until the top is golden brown and the filling is bubbling around the edges.
Remove from oven and let the bars cool completely in the pan on a wire rack. This allows the filling to set and makes slicing easier.
Slice into squares and serve, enjoying the contrast of crispy topping, tender fruit, and flaky crust.
