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1
Position a rack in the middle of the oven and preheat the oven to 325F Butter an 11-inch ring mold or a 12-cup (10-inch) Bundt pan, and place in a deep roasting pan.
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2
Sift together the sugar and cocoa into a medium bowl.
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3
Shift in cinnamon, if using.
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4
In the bowl of a stand mixer fitted with the whisk attachment, whip the whites on medium speed until soft peaks form, 5 to 7 minutes.
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5
Do not overbeat.
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6
Meanwhile, bring a medium saucepan of water to a boil for the water bath.
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7
Remove the bowl from the mixer, and top the whites with the cocoa mixture.
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8
This will look like a lot to incorporate, but the batter will come together.
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9
Slowly and gently fold the ingredients together, reaching to the bottom of the bowl to incorporate all the whites.
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10
Pour the batter into the prepared pan.
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11
Spread the batter into the corners with a rubber spatula.
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12
Pour enough boiling water into the roasting pan to come 2 to 3 inches up the sides of the mold.
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13
Bake for 45 minutes to 1 hour, or until a skewer inserted in the center of the cake comes out clean.
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14
The cake will puff up as it bakes, then shrink back as it cools.
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15
Carefully transfer the mold to a cooling rack, and cool completely in the pan.
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16
Run a knife around the edges of the pan and unmold the cake onto a serving plate.
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17
Serve with whipped cream and, if desired, a sprinkling of cacao nibs.
