Preheat the oven to 350°F or 180°C. Line an 8x8 baking dish with parchment paper. I recommend letting the parchment paper slightly hang over the sides for easy removal after baking. Set aside. Wash and dice the strawberries into small cubes. Set aside.
In a separate bowl, combine the flour, salt, and baking powder and set aside as well.
In a microwave-safe bowl, carefully melt the butter on your microwave's soften/melt setting. Or you can add the butter to a medium-sized pan and melt it on the stove over low heat. Once melted, add the brown sugar, lemon juice, and vanilla extract (or scrape out the seeds of one vanilla bean).
Whisk in the egg until fully incorporated. A regular whisk works great!
Add the flour mixture to the wet ingredients and mix until combined.
Then put in the cut-up strawberries and carefully fold them in.
Pour the batter into the lined baking dish, and with a rubber spatula, level it.
Bake for 25-30 minutes. The middle might still be a little soft, but that’s ok if the edges are golden brown.
Let them cool before removing from the pan.