Preheat oven to 350°F (175°C). Lightly butter an 8x8 inch square baking pan and line it with parchment paper, letting the paper hang over the edges for easy removal.
Make the crumb topping: In a medium bowl, whisk together melted butter, granulated sugar, and light brown sugar until crumbly. Set aside in the fridge until ready to use.
Macerate the strawberries: In a separate medium bowl, toss together chopped strawberries, lemon juice, sugar, and flour until the strawberries are well coated. Set aside.
Make the cake batter: In a stand mixer bowl, cream together softened butter and granulated sugar until light and fluffy. Slowly add the whisked eggs, one at a time, mixing well after each addition. Beat in the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt. Alternately add the dry ingredients and buttermilk to the wet ingredients, beginning and ending with the dry ingredients. Mix until just combined.
Pour the batter into the prepared baking pan and spread it into an even layer.
Top the batter with the macerated strawberries, spreading them evenly.
Sprinkle the chilled crumb topping evenly over the strawberries.
Bake for 55-60 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Let the cake cool in the pan on a wire rack for 20 minutes, then carefully transfer it to the wire rack to cool completely. Dust with powdered sugar before serving.