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1
Note: For the above measurement of flour, I recommend a blend of 2 and 1/3 cups brown rice flour, 1 cup plus 2 tablespoons potato starch, 2/3 cup tapioca starch, but you can use any all purpose flour blend you like.
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2
If your blend already has it, omit the xanthan gum.
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3
For the cake: Preheat oven to 350 degrees F. Grease a 9x13 sheet cake pan (I prefer to use glass since you will be serving it in this).
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4
Combine flour(s), xanthan gum, baking powder, baking soda, and salt in a bowl and whisk together to break up any lumps.
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5
In the bowl of your stand mixer (or in a large mixing bowl with a hand mixer), beat the butter and sugar together until the sugar has dissolved and the mixture is light and fluffy (about 2 minutes).
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6
Beat in the vanilla extract.
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7
Add the eggs and beat well.
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8
Beat in the buttermilk until just combined.
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9
Add the dry ingredients 1/3 at a time, mixing until incorporated between each addition.
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10
Spread the batter evenly into the prepared pan (batter will be thick but do your best!).
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11
Bake 3540 minutes until an inserted toothpick comes out clean.
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12
Cool the cake on a wire rack until room temperature.
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13
Pierce the cake repeatedly with a fork about every 1/2 inch (or just get crazy!).
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14
Whisk the condensed milk, evaporated milk, and whole milk together and pour slowly over the cake to give it time to absorb.
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15
Cover with plastic wrap and refrigerate for one hour.
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16
Whip the heavy cream, powdered sugar, vanilla, and rum until you reach a stiff and spreadable consistency.
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17
Spread over the top of the chilled cake.
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18
You can serve the cake immediately, but I like to refrigerate it for another 2030 minutes.
