1For the filling and topping: Whisk sugars, salt, nuts and butter in a large bowl to combine. Add flour and stir with a rubber spatula or wooden spoon until mixture is cohesive. Set aside to cool to room temperature. 10 to 15 minutes.
2For the cake: Put oven rack in upper middle position and preheat oven to 350 degrees. Grease and lightly flour a tube pan.
3In an electric mixer with a paddle attachment mix, flour, sugar baking soda and salt on low speed. With motor running on low add butter 1 piece at a time. Beat until no pieces remain and mixture resembles moist crumbs. Add
eggs, egg yolk, vanilla and buttermilk. Beat on medium high speed until light and fluffy about 1 minute. Scraping when necessary. Stir in chocolate chips.
4Spread half of the batter in pan with rubber spatula. Sprinkle with half the topping mixture. Carefully spread remaining batter on filling. Sprinkle with remaining topping mixture, squeezing and rolling between fingers to make larger crumbs.
5Bake until crumbs are golden brown and wooden skewer inserted in center of cake comes out clean, 50-55 minutes. Cool on wire rack, about 20 minutes. remove from tube pan and invert on plate, place serving plate on top and reinvert. Let cool completely. Dust with confectioners sugar before serving