Preheat the oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
Add in the cold, cubed butter and use a pastry cutter or your fingers to cut it into the flour mixture until it resembles coarse crumbs.
Pour in the milk and vanilla extract, stirring gently until just combined. Be careful not to overmix; it’s okay if there are a few lumps.
Spread half of the batter into the prepared baking pan, smoothing it out evenly with a spatula.
In a separate bowl, combine the sliced strawberries, lemon juice, and cornstarch. Mix until the strawberries are well coated, then pour this filling over the batter in the pan.
Drop spoonfuls of the remaining batter over the strawberry mixture, trying to cover as much as possible. It doesn't have to be perfectly smooth.
Bake in the preheated oven for 30-35 minutes, or until the top is golden and a toothpick inserted into the center comes out clean.
Once baked, allow to cool in the pan for about 10 minutes before lifting out using the parchment paper. Transfer to a wire rack to cool completely.
Once cooled, cut into bars and serve topped with a dollop of whipped cream.
Notes
Allow to cool completely before cutting for best results.