Cinnamon-Apple Babka

Prepare the Dough:

1. Whisk together warm water, sugar, and yeast in a medium bowl; let stand until foamy, about 5 minutes. Place salt and 3 cups of the flour in bowl of a stand mixer fitted with the paddle attachment. With mixer running on low speed, add yeast mixture and melted butter, beating just until combined, about 30 seconds. Turn off mixer; remove paddle attachment, and attach dough hook attachment. Beat mixture on medium-low speed until Dough is smooth and elastic, 7 to 12 minutes, beating in up to remaining 1/2 cup flour, 1/2 to 1 teaspoon at a time, if needed to achieve desired consistency. Coat a large bowl with cooking spray. Transfer Dough to prepared bowl, turning to grease top. Cover and let rise in a warm (75ºF), draft-free place until doubled in size, about 1 hour, 30 minutes.

Prepare the Filling:

1. Toss together apple, brown sugar, melted butter, cornstarch, cinnamon, and ginger in a medium bowl until combined. Coat a 10-inch cast-iron skillet with cooking spray. Set aside.
   

2. Gently punch down Dough in bowl. Roll Dough out on a lightly floured work surface into a 22- x 14-inch rectangle. Sprinkle and spread Filling evenly over Dough, carefully pressing to adhere and leaving a 1-inch border on long sides. Starting at 1 long side, roll Dough up, jelly-roll style, into a log, lifting the dough as needed to prevent liquid from slipping out. Using a serrated knife, cut log in half lengthwise. Arrange dough pieces side by side, cut sides up, on work surface. Carefully twist Dough pieces together, keeping cut sides facing up. (This process can be messy; if Filling spills onto Dough and work surface.) Shape twisted Dough into a 9-inch ring, and tuck ends under. Place in prepared skillet (see Tip). Secure ends under again, and tuck any apple slices back in, if needed. Cover with plastic wrap, and let rise in a warm, draft-free place until almost doubled in size, about 45 minutes. Preheat oven to 350°F.

3. Remove plastic wrap from skillet; place skillet on a rimmed baking sheet. Bake in preheated oven until babka is golden brown and an instant-read thermometer inserted into thickest portion of bread registers 190ºF to 205ºF, 30 to 35 minutes, loosely covering with aluminum foil during final 8 to 10 minutes bake time if needed to prevent overbrowning. Transfer skillet to a wire rack, and let cool 15 minutes. Whisk together powdered sugar and milk in a medium bowl until smooth. Drizzle over babka. Serve immediately. Babka may be wrapped in plastic wrap or aluminum foil or placed in an airtight container and stored at room temperature up to 3 days.