1 stick plus 5 tablespoons unsalted butter, plus more for pan
1 cup sugar
2 cups flour
1 teaspoon Kosher salt
Filling
3 cups blueberries
½ cup sugar
2 tablespoons flour
1 tablespoon fresh lemon juice
zest of one lemon
Instructions
Preheat oven to 375 degrees. Butter 8 x 8 x 2-inch cake pan. Line with parchment paper, leaving a 2-inch overhang on 2 sides. Butter parchment paper. For making the crust, beat butter and sugar until light and fluffy, about 3 minutes. Scrape down the sides of the bowl. Add flour and salt and mix until dough forms clumps but does not completely hold together. Press all but ¾ cup of the dough mixture into the bottom and 1 inch up the sides of the prepared pan.
To make the blueberry filling: Stir together blueberries, sugar, flour, lemon juice, lemon zest and salt. Pour onto crust. Crumble remaining flour mixture evenly over top to create clumps. Bake until bubbling in the center and the crust is golden brown (about 70 minutes). Let cool for about 20 minutes. Remove from pan and let cool completely for one hour before cutting into squares.