Crumb Buns

• For the cake:
• Place oven rack to middle position and heat oven to 350°F.
• Grease 13 by 9-inch baking dish.
• In bowl of stand mixer fitted with dough hook, combine flour, milk, sugar, egg, yeast, and salt.
• Knead on low speed until dough comes together, about 2 minutes.
• With the mixer running, add butter 1 piece at a time.
• Increase speed to medium-high and continue to knead until dough forms stretchy, web-like strands on sides of bowl, about 6 minutes longer (dough will be soft and sticky).
• Using greased rubber spatula, transfer dough to prepared dish.
• Using your floured hands, press dough into even layer to edges of dish.
• Cover dish tightly with plastic wrap and let dough rise at room temperature until slightly puffy, about 1 hour.

Topping

• minutes before dough has finished rising, whisk melted butter, granulated sugar, brown sugar, cinnamon, and salt together in bowl.
• Add flour and stir with rubber spatula or wooden spoon until mixture forms thick, cohesive dough; let sit for 10 minutes to allow flour to hydrate.
• If dough has pulled away from sides of dish after rising, gently pat it back into place using your floured fingers. Break topping mixture into rough 1/2-inch pieces using your fingers and scatter in even layer over dough in dish. (Be sure to scatter all crumbs even though it may seem like too much.)
• Bake until crumbs are golden brown, wooden skewer inserted in center of cake comes out clean, and cake portion registers about 215°F in center, about 35 minutes.
• Transfer dish to wire rack and let cake cool completely. Using spatula, transfer cake to cutting board; cut cake into 12 squares.
• Dust squares with confectioners’ sugar and serve.