Blueberry Buckle

So I bought a bunch of blueberries thinking I was going to make another blueberry coffee cake, but I ended up making this one and I'm glad I did. After checking Cook's Illustrated I realized I'd never made (or heard of) a buckle, so I gave it a shot. A buckle is basically a coffee cake, and this was definitely the best buckle/coffee cake I've ever made. The blueberries, lemon zest and cinnamon go perfectly together.

The recipe only makes a little bit of dough, and I couldn't believe that a whole quart of blueberries could be folded into it, but somehow it worked out. It also took forever to bake -- more like 75 minutes than 55 -- and it could have gone longer, since the bottom was a bit gummy. I'd say give it another few minutes once a tester comes out clean.

Streusel
• 1/2 cup unbleached all-purpose flour (2 1/2 ounces)
  
• 1/2 cup packed light brown sugar (3 1/2 ounces)
  
• 2 tablespoons granulated sugar
  
• 1/4 teaspoon ground cinnamon
  
• Pinch table salt
  
• 4 tablespoons unsalted butter (1/2 stick), cut into 8 pieces, softened but still cool
  
  Cake
• 1 1/2 cups unbleached all-purpose flour ( 7 1/2 ounces)
  
• 1 1/2 teaspoons baking powder
  
• 10 tablespoons unsalted butter (1 1/4 stick), softened but still cool
  
• 2/3 cup granulated sugar (about 4 3/4 ounces)
  
• 1/2 teaspoon table salt
  
• 1/2 teaspoon grated lemon zest
  
• 1 1/2 teaspoons vanilla extract
  
• 2 large eggs, room temperature
  
• 4 cups fresh blueberries (about 20 ounces), picked over

1. For the streusel: In standing mixer fitted with flat beater, combine flour, sugars, cinnamon, and salt on low speed until well combined and no large brown sugar lumps remain, about 45 seconds. Add butter and mix on low until mixture resembles wet sand and no large butter pieces remain, about 2 1/2 minutes. Transfer streusel to small bowl and set aside.
   
2. For the cake: Adjust oven rack to lower-middle position; heat oven to 350 degrees. Spray 9-inch round cake pan with 2-inch sides with nonstick cooking spray, line bottom with parchment or waxed paper round, and spray round; dust pan with flour and knock out excess.
   
3. Whisk flour and baking powder in small bowl to combine; set aside. In standing mixer fitted with flat beater, cream butter, sugar, salt, and lemon zest at medium-high speed until light and fluffy, about 3 minutes; using rubber spatula, scrape down bowl. Beat in vanilla until combined, about 30 seconds. With mixer running at medium speed, add eggs one at a time; beat until partially incorporated, then scrape down bowl and continue to beat until fully incorporated (mixture will appear broken). With mixer running on low speed, gradually add flour mixture; beat until flour is almost fully incorporated, about 20 seconds. Disengage bowl from mixer; stir batter with rubber spatula, scraping bottom and sides of bowl, until no flour pockets remain and batter is homogenous; batter will be very heavy and thick. Using rubber spatula, gently fold in blueberries until evenly distributed.
   
4. Transfer batter to prepared pan; with rubber spatula, using a pushing motion, spread batter evenly to pan edges and smooth surface. Squeeze handful of streusel in hand to form large cohesive clump; break up clump with fingers and sprinkle streusel evenly over batter. Repeat with remaining streusel. Bake until deep golden brown and toothpick or wooden skewer inserted into center of cake comes out clean, about 55 minutes. Cool on wire rack 15 to 20 minutes (cake will fall slightly as it cools).
   
5. Run paring knife around sides of cake to loosen. Place upside-down plate (do not use plate or platter on which you plan to serve the cake) on top of cake pan; invert cake to remove from pan, lift off cake pan, then peel off and discard parchment. Re-invert cake onto serving platter. Cool until just warm or to room temperature, at least 1 hour. Cut into wedges and serve.