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1
Preheat the oven to 325F.
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2
Line the bottom of a 9 x 3-inch round cake pan with a circle of parchment paper and coat both paper and sides lightly with oil.
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3
In a medium bowl, whisk together the flour, potato starch, arrowroot, cocoa powder, baking powder, baking soda, xanthan gum, and salt.
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4
Add 1/2 cup oil and the agave nectar, applesauce, vanilla, and hot water to the dry ingredients and stir until the batter is smooth.
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5
Pour the batter into the prepared pan and bake on the center rack for 20 minutes.
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6
Remove the pan from the oven and spoon the Chocolate Crumb over the cake, gently patting it down.
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7
Return the pan to the oven and bake the cake for an additional 15 minutes.
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8
The finished crumb topping will be slightly crisp to the touch, and the cake will be firm.
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9
Let the cake stand in the pan for 20 minutes, then gently run a knife around the edges.
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10
Cover the top of the pan with a cutting board and flip over.
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11
Carefully lift the pan away and re-invert the cake onto a serving plate.
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12
Pour the chocolate sauce into a squeeze bottle and drizzle it evenly over the top of the cake in a zigzag pattern from one edge to the other.
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13
Rotate the cake 180 degrees and drizzle it again.
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14
Cover the cake with a dome and store at room temperature for up to 3 days.
