Preheat the oven to 350°F (175°C). Line a 9×9-inch baking pan with parchment paper and set aside.

In a large bowl, whisk together the flour, baking powder, and salt. Add the cold butter and use a pastry cutter to create a crumb-like mixture. Alternatively, pulse the mixture in a food processor until pea-sized crumbs form, about 20 seconds.

In a separate large bowl, whisk together the brown sugar, egg, and vanilla until combined. Slowly add the flour mixture to the wet mixture and use a rubber spatula or your hands to combine into a crumbly dough.

Press 2/3 of the mixture firmly into the bottom of the prepared pan, making sure it is compact to form a sturdy crust.

In a medium bowl, stir together the chopped strawberries, granulated sugar, and cornstarch. Spoon the strawberry mixture evenly over the crust.

Sprinkle the remaining crumb mixture evenly over the strawberry layer.

Bake for 40–45 minutes, or until the top is golden brown and the strawberry layer is bubbling at the edges.

Remove from the oven and allow to cool completely at room temperature. Cut into 1½-inch squares and serve.