Apple Fritter Coffee Cake

Instructions

1. 1Preheat the oven to 350°F (175°C). Grease a 9x9-inch light-colored metal pan. Line it with two long sheets of parchment crossed in opposite directions, covering the bottom and all four sides with a noticeable overhang on every side. This keeps the caramelized edges from sticking and gives you handles to lift the cake out.
2. 2Make the crumble: combine the all-purpose flour, brown sugar, granulated sugar, cinnamon, salt, cold butter, and vanilla bean paste. Mix everything evenly with your fingertips, squeezing it into large clusters. Refrigerate while you prepare the remaining components.
3. 3Make the cinnamon swirl: stir together the brown sugar, melted butter, cinnamon, all-purpose flour, and salt until evenly combined. Set aside.
4. 4Peel and core the Granny Smith apple, then weigh 200 g and cut into roughly 1/2-inch pieces. If the cut surfaces look visibly wet, blot lightly with a paper towel.
5. 5In a large bowl, whisk the brown sugar, granulated sugar, oil, Greek yogurt, milk, and vanilla bean paste until smooth. Add the all-purpose flour, cornstarch, baking powder, baking soda, salt, and nutmeg directly over the wet ingredients. Whisk gently just until no dry streaks remain. Fold in the apple pieces without overmixing.
6. 6Spread just under half the batter evenly into the prepared pan. Spread the cinnamon paste evenly across the surface. If you like, make a few light passes with a knife to swirl it slightly.
7. 7Spoon the remaining batter over the cinnamon layer, then gently connect and smooth the spoonfuls without disturbing the layer underneath.
8. 8Scatter the chilled crumble evenly over the top, keeping it in large clusters to create a textured surface with crevices for the glaze. Finish with a generous sprinkle of clear coarse sanding sugar.
9. 9Bake with a foil-lined sheet pan on the rack underneath to catch drippings. In my light-colored metal pan, I baked for 45 minutes, tented loosely with foil, then baked another 15-20 minutes. Check the top before 45 minutes, especially with dark aluminum or glass, and tent sooner if it is browned enough. I haven't tested glass; the center will likely need longer to bake through.
10. 10Use doneness cues rather than the clock: the center must be fully set, and a tester inserted into a cake portion should come out clean or with moist crumbs, not wet batter. Check the center with an instant-read thermometer, avoiding apple pieces and the cinnamon ribbon; mine baked through at 210-215°F. The fresh apples release moisture into the layers. Keep baking if the center is still wet, even if you have reached the end of the time range.
11. 11Rest the cake in the pan for at least 30 minutes. Use the parchment overhangs to carefully lift it onto a wire rack set over a tray. Gently peel the paper away from the sides. Let it cool longer if it is still hot; it should be warm and sturdy enough to handle before glazing.
12. 12Whisk the 220 g powdered sugar, 2 teaspoons vanilla bean paste, and 70 g milk together until smooth.
13. 13Pour about half the glaze over the top. Carefully support the cake underneath and gently tip it onto its side to let the excess glaze fall onto the tray. I use my forearm to keep the cake from sliding. Keep the coating very thin, like an apple fritter.
14. 14Coat the sides with the remaining glaze, allowing excess to drip away so the top and all four sides have a thin coating. Return the cake to an upright position.
15. 15Refrigerate for at least 20 minutes to allow the icing to set before slicing.