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1
Position an oven rack on the middle rung.
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2
Heat the oven to 350 degrees (180C).
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3
Lightly grease and flour the bottom and sides of a 9-by-2-inch (75 cm-by-5 cm) round cake pan, tapping out the excess flour.
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4
In a medium bowl, combine the flour, baking powder, baking soda, cinnamon, and salt.
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5
Whisk until well blended.
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6
In a large bowl, combine the butter and sugar.
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7
Beat with an electric mixer (stand mixer fitted with the paddle attachment or hand held mixer) on medium speed until well blended.
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8
Add the eggs one at a time and beat just until blended.
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9
Add the vanilla with the second egg.
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10
Using a rubber spatula, fold the dry ingredients into the butter mixture in 3 batches alternately with the sour cream, beginning and ending with the dry ingredients.
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11
Scrape the batter into the prepared pan and spread evenly.
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12
Bake for 10 minutes.
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13
As soon as you put the cake in the oven, make the topping.
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14
In a small bowl, combine the blueberries, sugar, flour, and cinnamon.
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15
Mix the ingredients together with a fork, lightly crushing the blueberries.
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16
After the cake has baked for 10 minutes, sprinkle the topping evenly over the top of the cake.
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17
Continue baking until a toothpick or cake tester inserted in the center of the cake comes out clean, about 30 minutes longer.
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18
Transfer the cake to a rack to cool for 10 minutes.
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19
Run a knife around the inside edge of the pan to loosen the cake.
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20
Using a thick, dry dish towel to protect your hands, invert a large, flat plate on top of the cake pan and, holding both the pan and the plate, invert them together.
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21
Lift the pan off the cake.
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22
Invert a flat serving plate on the bottom of the cake and invert the cake one more time so that the blueberries are on top.
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23
Serve warm or at room temperature.
