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1
For the streusel:
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2
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.
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3
Add butter and mix on low until mixture resembles wet sand and no large butter pieces remain, about 2 1/2 minutes.
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4
Transfer streusel to small bowl and set aside.
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5
For the cake:
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6
Adjust oven rack to lower-middle position; heat oven to 350 degrees. Spray 9-inch round cake pan*(I used a shallow rectangle white dish and it cut neat squares) with 2-inch sides with nonstick cooking spray.
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7
Whisk flour and baking powder in small bowl to combine; set aside.
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8
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.
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9
Beat in vanilla until combined, about 30 seconds.
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10
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.
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11
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.
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12
Using rubber spatula, gently fold in blueberries until evenly distributed.
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13
Transfer batter to prepared pan; with rubber spatula, using a pushing motion, spread batter evenly to pan edges and smooth surface.
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14
Sprinkle streusel evenly over batter.
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15
Bake until deep golden brown and toothpick or wooden skewer inserted into center of cake comes out clean, about 55 minutes.
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16
Cool on wire rack 15 to 20 minutes (cake will fall slightly as it cools).
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17
ool until just warm or to room temperature, at least 1 hour. Cut into wedges and serve.
