For the cake
3/4 cup (6 fluid ounces) boiling water
1/4 cup (2 fluid ounces) strong brewed coffee (See Recipe Notes)
1/4 cup (20 g) unsweetened cocoa powder (natural or Dutch-processed)
1 ounce dairy-free dark chocolate, chopped (optional)
2/3 cup (150 g) mayonnaise (full fat, regular mayo)
3/4 cup (150 g) granulated sugar
1 /4 teaspoon kosher salt
1 teaspoon pure vanilla extract
1 1/4 cups (175 g) all purpose gluten free flour (I used Better Batter)
Heaping 1/2 teaspoon xanthan gum (omit if your blend already contains it)
1/4 cup (36 g) cornstarch
1 teaspoon baking soda
6 ounces dairy-free semi-sweet chocolate chips (optional)
For chocolate topping (optional)
10 ounces dairy-free dark chocolate, chopped
3/4 cup (6 fluid ounces) canned coconut cream (See Recipe Notes)
For the brewed coffee
You can use decaffeinated coffee. You can replace the brewed coffee with more water, but I don’t recommend it. The coffee enhances the chocolate flavor without tasting like coffee.
For the coconut cream in the topping
If you don’t have to be dairy-free, use heavy whipping cream in the same amount. If you do use the coconut milk, do not use “light” coconut milk, which is just thick coconut milk with water added.
Preheat your oven to 350°F. Grease and line an 8-inch round or square baking pan. Set the pan aside.
In a medium-size, heat-safe mixing bowl or measuring cup, place the boiling water and brewed coffee and the cocoa powder, and whisk until well-combined. The cocoa powder will resist combining, so just keep whisking.
Add the (optional) chopped chocolate, and mix until melted and smooth. Add the mayonnaise, sugar, salt, and vanilla, and whisk until well-combined.
In a large bowl, place the flour, xanthan gum, cornstarch, baking soda, and about 5 ounces of the (optional) chocolate chips, and mix to combine and coat the chips in the flour. Create a well in the center of the dry ingredients, and add the wet mixture. Mix until very smooth and well-combined. The batter will start off very thin, but will thicken a bit as you stir. Keep mixing until that happens.
Transfer the cake batter to the prepared pan, and smooth into an even layer using a moistened spatula or broad, flat knife. Sprinkle the remaining (optional) chocolate chips evenly over the top, and bang the cake a few times on the counter to help the chips adhere.
Place the pan in the center of the preheated oven and bake for about 30 minutes, or until done. Doneness should be determined by a few things: the cake should be puffed and rounded at the edges. It also shouldn’t jiggle when moved back and forth, and a toothpick inserted in the center should come out mostly clean (and certainly not wet).
Remove the cake from the oven, place the pan on a wire rack and allow to cool completely in the pan. To make it easier to slice, you can chill the pan in the refrigerator.
To make the topping, place the chopped dark chocolate in a small, heat-safe bowl. Place the coconut cream in a small, heavy-bottom saucepan and melt over a low flame. Pour the hot cream over the chopped chocolate and allow it to sit, undisturbed, for about 5 minutes before whisking until completely smooth. Pour the glaze directly over the cooled cake, and allow it to set at room temperature.
To whip the chocolate ganache into frosting, allow it to cool at room temperature, then cover and refrigerate it until beginning to set (about 20 minutes). Using a handheld mixer or a stand mixer fitted with the whisk attachment, whip the frosting until lighter in color and relatively fluffy (about 3 minutes). Frost the cakes as desired, and then slice and serve.
Cake recipe adapted heavily from The New York Times chocolate snack cake.