Blueberry Fritter Coffee Cake

Instructions

1. 1Preheat the oven to 350°F. Line a 9x9-inch metal baking pan with parchment paper, covering the bottom and all four sides anywhere the batter will touch. Leave overhangs for lifting the cake out. The parchment protects the caramelized edges from being scraped away when you remove the cake.
2. 2Make the crumble: combine the all-purpose flour, brown sugar, granulated sugar, cinnamon, and salt in a medium bowl. Add the cold cubed butter and vanilla bean paste. Work together with your fingertips or a pastry cutter until moist crumbs form, then squeeze into large clusters. Refrigerate while you prepare the filling and batter.
3. 3Make the cinnamon filling: stir the brown sugar, melted butter, cinnamon, all-purpose flour, and salt together in a small bowl until you have a thick, smooth paste. Set aside.
4. 4Make the batter: whisk the granulated sugar, oil, plain unsweetened yogurt, milk, vanilla bean paste, and blueberry emulsion in a large bowl until smooth. Add the all-purpose flour, cornstarch, baking powder, baking soda, salt, and nutmeg directly over the wet ingredients. Mix just until no dry flour remains. Do not add the blueberries yet.
5. 5Gently toss the dried blueberries with the 1 tablespoon all-purpose flour for coating. Spread a little over half the batter into the prepared pan, taking it into every corner. Scatter half the coated blueberries evenly over the batter, reserving the other half for the top layer.
6. 6Spoon the cinnamon filling over the batter and berries. Gently spread it into an even layer all the way to the parchment-lined edges. Do not leave a border - the filling at the sides creates the caramelized edge.
7. 7Fold the remaining 85 g blueberries into the batter left in the bowl, taking care not to crush them. Dollop this batter over the cinnamon filling, then gently spread it into an even layer without disturbing the filling underneath.
8. 8Scatter the chilled crumble evenly over the entire surface, keeping it in large clusters. These create a textured top with spaces for the glaze to settle into after baking.
9. 9Bake at 350°F for about 45 minutes before checking the topping. Once the crumble and edges are deeply golden, loosely tent the pan with foil. Continue baking for about 10-20 minutes, or longer as needed, until the center reaches 210-215°F on an instant-read thermometer. Some ovens may need 20-30 minutes longer than my approximate 55-minute bake. If the center reads about 203°F, allow roughly 10 more minutes before checking; at 207°F, check again in about 5 minutes. The edges should be a deep caramel brown.
10. 10Rest the cake in the pan for at least 30 minutes. Lift it out using the parchment and transfer to a cooling rack. If it feels too delicate to handle, let it cool longer before the next step.
11. 11Remove the parchment: place a clean wire rack or sheet pan over the top of the cake. Holding the cake securely between the two surfaces, carefully invert it so the crumble faces down. Gently peel the parchment from the exposed base. Place a cooling rack against the base and invert again so the crumble faces up. Set the rack over a tray or parchment to catch the glaze.
12. 12Whisk the powdered sugar, milk, vanilla bean paste, and optional pinch of salt until smooth. Pour the thin glaze over the slightly warm cake, letting it coat the crumble and run down the sides. Support the cake securely and carefully tip it to let the excess drip off. You want a very thin coating; much of the glaze will collect underneath and is not meant to stay on the cake.
13. 13Let the glaze set completely before slicing. For a crackly glaze with a warm center, refrigerate for 20-30 minutes, or freeze for 10-15 minutes if you are in a hurry, then check. Give a thicker coating more time to set.