Make the crumb topping: Mix together flour, granulated sugar, brown sugar, cinnamon, and salt in a medium bowl. Pour warm melted butter over mixture; using your hands, mix until medium to large clumps form. Make the cake: Preheat oven to 325°F. Butter a 9-by-13-inch baking pan, line with parchment with overhang on both long sides, and butter parchment. Whisk together flour, baking soda, and salt in a medium bowl. With an electric mixer on medium speed, beat butter and granulated sugar until pale and fluffy, about 2 minutes. Add eggs and yolks, 1 at a time, beating well after each addition; mix in vanilla. Add flour mixture in 3 additions, alternating with 2 additions of buttermilk; beat until well combined. Transfer batter to prepared pan; spread evenly with an offset spatula. Sprinkle crumb-topping mixture evenly over batter. Bake until golden brown and a cake tester comes out clean, about 1 hour. Transfer pan to a wire rack to cool slightly, about 15 minutes. Dust with confectioners’ sugar. Transfer cake, with parchment, to wire rack. Serve warm or at room temperature. (Cake can be stored at room temperature, covered, up to 5 days.)