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1
Set the oven at 350 degrees F. Butter a 9-inch round cake pan or 8-inch square baking pan. Take a round of parchment paper that fits the bottom of the pan, place that into the pan, butter it and dust the parchment and sides with cocoa powder; set aside.
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2
In a medium bowl, sift the flour, cocoa powder, baking powder, and salt to combine. Whisk together; set aside.
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3
In a large bowl, whisk the egg, butter, and sugar together until thickened and thoroughly mixed. Stir in the milk, espresso, and vanilla extract.
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4
Pour the chocolate syrup into the egg mixture, and stir to combine.
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5
Sprinkle the flour mixture over the top of the syrup mixture, and gently fold the dry ingredients into the wet ingredients just until combined. Do not overmix.
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6
Pour the batter into the prepared baking pan, and gently tap the pan on the surface of the counter to tap out any air bubbles. Place in the middle rack of the oven, and bake for 25 minutes.
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7
Halfway through baking, sprinkle half of the sea salt onto the cake. Once the cake is set and begins to pull away from the sides, remove from the oven and place on a cooling rack. Sprinkle the remaining sea salt on the top, allow the cake to cool, then slice and serve.
