Blackberry Crumb Bars

1) Preheat oven to 350 degrees F. Butter an 8-inch square baking pan. Line bottom of pan with parchment paper, leaving an overhang of parchment paper on two sides; butter and flour the paper, tapping out excess flour.
2) Make topping: In a medium bowl, whisk together melted butter, brown sugar, and 1/4 teaspoon salt; add 1 cup flour, and mix with a fork until large moist crumbs form. Refrigerate topping until ready to use.
3) In a medium bowl, whisk together remaining 3/4 cup flour, baking powder, and remaining 1/4 teaspoon salt; set aside.
4) In a large bowl, using an electric mixer, beat room-temperature butter, confectioners’ sugar, and vanilla until light and fluffy; add eggs, one at a time, beating well after each addition. Reduce speed to low; mix in the flour mixture.
5) Spread batter evenly into the prepared pan; sprinkle with blackberries, white chocolate chips, then add the chilled topping.
6) Bake until golden and a toothpick inserted in center comes out with moist crumbs attached, 40 to 45 minutes.
7) Cool completely in pan. Then, using paper overhang, lift cake onto a work surface; cut into 16 squares.