(very) chocolate chippy crumb cake

Ingredients

• 1 1/2 cups all purpose flour
• 1 cup packed light brown sugar
• 1/2 cup sugar
• 3/4 cup chopped walnuts (I like them chopped fairly small here)
• 1/2 teaspoon kosher salt
• 11 tablespoons (1 stick plus 3 tablespoons) unsalted butter cut into pieces
• 1 1/2 teaspoons vanilla extract
• 1 cup mini semisweet chocolate chips
• 2 3/4 cup all purpose flour
• 1/4 cup unsifted cake flour
• 1 1/2 teaspoons baking powder
• 1/2 teaspoon baking soda
• 1 teaspoon kosher salt
• 2 sticks unsalted butter, softened at room temp
• 3/4 sugar
• 1/4 cup packed light brown sugar
• 1 tablespoon vanilla extract
• 3 large eggs (bring to room temp)
• 1 cup buttermilk (bring to room temp)
• 2 cups mini chocolate chips (semisweet)
• confectioners sugar (optional)