Yeasted Apple Coffee Cake

Ingredients

• 6 tablespoons unsalted butter, melted, slightly cooled, plus more
• 1 1/4-ounce envelope active dry yeast (about 2 1/4 teaspoons)
• 2/3 cup (packed) light brown sugar, divided
• 1 large egg, room temperature
• 3 cups all-purpose flour, divided
• 1/2 cup sour cream, room temperature
• 2 teaspoons finely grated orange zest
• 1/3 cup fresh orange juice
• 2 teaspoons baking powder
• 1 teaspoon kosher salt
• 1/2 cup all-purpose flour
• 1/2 cup old-fashioned oats
• 1/3 cup (packed) light brown sugar
• 2 tablespoons granulated sugar
• 1 teaspoon ground cinnamon
• Kosher salt
• 6 tablespoons unsalted butter, melted, slightly cooled
• 2 pounds firm baking apples (about 4 large), halved, cored, very thinly sliced
• 1 1/2 cups powdered sugar
• 2 tablespoons (or more) fresh orange juice