Apple Fritter Cake

Name: Apple Fritter Cake
Ingredients: 2 1/4 cups all-purpose flour; 3/4 cup granulated sugar; 2 1/2 teaspoons baking powder; 1 teaspoon ground cinnamon; 1/2 teaspoon kosher salt; 1/4 teaspoon baking soda; 12 tablespoons (1 1/2 sticks) unsalted butter; 3 large eggs; 3/4 cup buttermilk; 2 teaspoons vanilla extract; 1/2 cup packed dark brown sugar; 2 teaspoons ground cinnamon, divided; 1 teaspoon all-purpose flour; 1 1/2 pounds Granny Smith or Honeycrisp apples (4 medium); 2 tablespoons granulated sugar; 1/2 cup powdered sugar; 2 teaspoons milk, apple cider, or unfiltered apple juice, plus more as needed