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1
Position an oven rack in the center of the oven, and preheat to 350 degrees F. Line the bottom of a 9-inch round cake pan with a parchment circle.
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2
Butter the parchment and the sides of the pan.
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3
For the cookie layer: Whisk together the flour, baking soda and salt in a large bowl; set aside.
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4
Beat the butter and both sugars with an electric mixer on medium-high speed in a large bowl until light and fluffy, about 4 minutes.
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5
Add the egg, and beat until incorporated.
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6
Beat in the vanilla.
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7
Scrape down the bowl as needed.
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8
Reduce the speed to medium, add the flour mixture and beat until just incorporated.
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9
Stir in the chocolate chips.
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10
Press the cookie dough into an even layer in the prepared cake pan, and bake until golden brown and a knife inserted in the center comes out clean, 25 to 30 minutes.
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11
Let the layer cool for about 10 minutes.
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12
It will collapse slightly as it cools.
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13
To make the layer even, press the bottom and sides down with the bottom of a measuring cup.
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14
For the cake layer: Whisk together the flour, baking powder and salt in a medium bowl; set aside.
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15
Beat the granulated sugar and oil with an electric mixer on medium-high speed in a large bowl until light in color and fluffy, about 5 minutes.
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16
Beat in the eggs one at a time.
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17
Beat in the vanilla.
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18
Alternate folding the flour mixture and the milk into the batter with a spatula, adding the flour in three additions and the milk in two, starting and ending with the flour, until just smooth.
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19
Stir in the sprinkles.
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20
(The cake batter will be on the thin side, like a thick pancake batter.)
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21
Pour the cake batter over the cookie layer, and bake until the middle of the cake springs back when pressed and a knife inserted in the center comes out clean, 1 hour to 1 hour 10 minutes.
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22
Run a knife around the edge of the cake, and let cool completely in the pan on a rack.
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23
Transfer the cake from the pan to a serving plate, with the cookie layer on the bottom.
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24
For the frosting: Beat the cream cheese and granulated sugar with an electric mixer on medium-high speed in a large bowl until smooth and all the sugar has dissolved (rub some between your fingers; if it's gritty, keep beating).
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25
Add the cream and vanilla, and continue to beat until medium peaks form.
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26
Frost the cake, and decorate with more sprinkles.
