Sourdough Crumb Cake

Name: Sourdough Crumb Cake
Prep time: 30 min
Cook time: 45 min
Total time: 1 h 15 min
Cuisine: American
Ingredients: 6 ¾ oz cake flour (1 ½ cups, see note); 5 ¼ oz brown sugar (⅔ cup); ¼ teaspoon salt; 2 teaspoons cinnamon; 4 oz unsalted butter (cool room temperature); 8 oz sourdough discard (1 cup); 1 large egg; 1 large yolk; 1 tablespoon vanilla extract; 6 ¾ oz cake flour (1 ½ cups); 6 oz granulated sugar (¾ cup); 1 ½ teaspoons baking powder; 4 oz unsalted butter (room temperature); 4 oz buttermilk (½ cup, room temperature)