Sourdough Coffee Cake Recipe

Name: Sourdough Coffee Cake Recipe
Prep time: 45 min
Cook time: 30 min
Total time: 1 h 15 min
Cuisine: American
Ingredients: 8 oz active sourdough starter (1 cup, 100% hydration); 4 oz whole milk (½ cup, warmed to 100°F); 10 oz all-purpose flour (2 cups, see note); 3 oz granulated sugar (⅓ cup); 2 oz unsalted butter (melted and cooled to room temperature); 1 large egg (room temperature); 1 teaspoon vanilla extract; ½ teaspoon salt; ½ teaspoon cinnamon; 3 oz brown sugar (⅓ cup); 4 oz walnuts (1 cup); 2 teaspoons ground cinnamon; ⅛ teaspoon table salt; 2.5 oz all purpose flour (½ cup); 2 oz unsalted butter (softened to room temperature); 1 egg (for egg wash); 4 oz confectioner's sugar (1 cup); 1 oz whole milk (2 tablespoons)