Cook time 30 minutes
Yield: Serves or Makes 16 bars
Preheat oven to 350°F and line an 8-inch square baking pan with parchment paper. Spray sides with non-stick cooking spray.
To brown butter, place butter in a heavy-bottomed pot. Melt on medium until it fizzles and spits and the solids start to turn a golden brown. Swirl every once in a while to make sure you haven’t burnt it. Once the butter smells nutty and you see that the bottom is covered with golden bits, remove from the heat. Place in a large heat proof bowl. Add sugar, brown sugar, vanilla, and lemon zest, and stir until combined.
In a medium bowl, whisk together flour, baking soda and salt. Add to butter mixture and fold until incorporated. Reserve ¾ cup of the crust for the topping, keeping it chilled in the meantime. In the lined baking pan, press remaining dough evenly into bottom of prepared pan. Bake crust for 15 minutes, until lightly golden and set. Transfer to a wire rack and cool for 15 minutes.
In the meantime, make the filling. Combine sugar, salt, lemon zest and cornstarch in a medium bowl. Add berries and toss to combine. Spoon over cooled crust and add reserved crumble over the fruit filling.
Cool completely in pan on a wire rack. Carefully lift parchment and place bars on a cutting board. Cut into squares with a sharp knife. Dust with powdered sugar if desired.