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1
Preheat oven to 300 degrees F (150 degrees C).
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2
Grease and flour a 10-inch springform pan, using gluten-free flour.
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3
In a bowl, sift together the gluten-free baking flour, cornstarch, cocoa powder, and baking powder.
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4
If mixture seems clumpy, sift again.
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5
Place the butter, avocado, applesauce, sugar, vinegar, buttermilk, and vanilla extract into the work bowl of a food processor, and pulse several times; process until well blended.
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6
Mix in the egg yolks, and process again.
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7
Scrape the mixture into a large bowl.
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8
In a separate mixing bowl, beat the egg whites with cream of tartar using an electric mixer until the whites form stiff peaks.
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9
Gently fold the egg whites into the avocado mixture, then fold in the flour mixture, being careful to retain as much fluffiness in the batter as you can.
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10
Gently mix in red food coloring.
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11
Pour the batter into the prepared springform pan.
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12
Bake in the preheated oven until the center is set and a toothpick inserted into the cake comes out clean, about 1 1/2 hours.
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13
Allow to cool.
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14
Since the cake is gluten-free, it may sink a little while cooling.
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15
When cool, remove from springform pan for decorating.
