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1
Heat the oven to 350F.
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2
Combine the butter and sugars in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high for 2 to 3 minutes.
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3
Scrape down the sides of the bowl, add the eggs, and mix on medium-high again for 2 to 3 minutes.
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4
Scrape down the sides of the bowl once more.
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5
On low speed, stream in the buttermilk, oil, and vanilla.
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6
Increase the mixer speed to medium-high and paddle for 4 to 6 minutes, until the mixture is practically white, twice the size of your original fluffy butter-and-sugar mixture, and completely homogenous.
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7
Dont rush the process.
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8
Youre basically forcing too much liquid into an already fatty mixture that doesnt want to make room for the liquid.
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9
Stop the mixer and scrape down the sides of the bowl.
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10
On very low speed, add the cake flour, baking powder, and salt.
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11
Mix for 45 to 60 seconds, just until your batter comes together and any remnants of dry ingredients have been incorporated.
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12
Scrape down the sides of the bowl.
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13
If you see any lumps of cake flour in there while youre scraping, mix for another 45 seconds.
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14
Pam-spray a quarter sheet pan and line it with parchment, or just line the pan with a Silpat.
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15
Using a spatula, spread the cake batter in an even layer in the pan.
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16
Give the bottom of your sheet pan a tap on the countertop to even out the layer.
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17
Sprinkle the chocolate chips evenly over the cake batter.
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18
Bake the cake for 30 to 35 minutes.
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19
The cake will rise and puff, doubling in size, but will remain slightly buttery and dense.
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20
At 30 minutes, gently poke the edge of the cake with your finger: the cake should bounce back slightly and the center should no longer be jiggly.
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21
Leave the cake in the oven for an extra 3 to 5 minutes if it doesnt pass these tests.
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22
Take the cake out of the oven and cool on a wire rack or, in a pinch, in the fridge or freezer (dont worry, its not cheating).
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23
The cooled cake can be stored in the fridge, wrapped in plastic wrap, for up to 5 days.
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24
There is a ton of liquid and fat in this amazing cake!
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25
If you do not do your due diligence to make sure that the batter is homogenous at each step (no streaks, discolorations, or other signs of separation/unincorporation), youll be sorry when your cake bakes out of its pan and all over the bottom of your oven.