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1
Set a rack in the middle of the oven and preheat to 325 degrees F. Spray 2 (9-inch) round pans with nonstick spray, line the bottom of the pan with a parchment paper round, spray the parchment with nonstick spray, and set aside.
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2
Whisk the flours, cocoa, baking soda, and salt together in a bowl and set aside.
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3
Whisk the buttermilk, food coloring, vinegar, and vanilla together in a small bowl and set aside.
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4
Combine the brown sugar and butter in the bowl of a stand mixer with the paddle attachment and cream on medium speed until lightened in color, 2 minutes.
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5
Stop the mixer and scrape down the sides of the bowl with a spatula.
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6
Return the mixer to medium speed and slowly add the eggs and beat until they are fully incorporated.
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7
With the mixer on low, add the flour mixture in 3 installments, alternating with the buttermilk mixture, beginning and ending with the flour mixture.
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8
Stop the mixer and scrape down the sides of the bowl between each installment.
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9
Mix on low speed until smooth, 30 to 45 seconds.
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10
Divide the batter evenly between the prepared pans and bake until the cake springs back when pressed or reaches an internal temperature of 205 degrees F, 30 to 35 minutes.
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11
Cool in the pans on a rack for 10 minutes, and then remove the cake from the pans and cool completely, about 1 hour, before frosting.
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12
Combine the cream cheese and butter on medium speed, just until blended, in the bowl of a stand mixer fitted with the paddle attachment.
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13
Stop and scrape down the sides of the bowl.
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14
Add the vanilla and salt and beat until combined.
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15
With the speed on low, add the powdered sugar in 4 batches, beating until smooth between each addition.
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16
Refrigerate for 5 to 10 minutes before using.
