Fudgy Gluten-Free Chocolate Cake With Hazelnut Frosting

Directions

1. Heat the oven to 350°F with a rack positioned in the center. Lightly grease the bottom and sides of an 8x3-inch round cake pan (see Author Notes if you only have a pan that’s 2 inches high) with nonstick spray or a bit of soft butter. Line the bottom with a circle of parchment paper.
2. In a large mixing bowl, whisk together the gluten-free flour, sugar, baking powder, and baking soda. Give it a really good mix, stirring for about 45 seconds (this evenly disperses the leavening agents and side steps any clumping).
3. Roughly chunk up the butter into small-ish cubes (it’s going to melt, so no need for precision here) and place in a small bowl. Add the oil, cocoa powder, salt and cinnamon to the same bowl.
4. Pour the hot coffee over the butter and cocoa mixture. (If your coffee isn’t piping hot, heat it up in a small pan or the microwave first.) Whisk everything together briskly to a smooth, glossy, runny paste.
5. Whisk in the sour cream, eggs and vanilla extract until fully incorporated.
6. Add this chocolate mixture to the dry ingredients and whisk till the flour is completely dissolved, about 60 seconds. The batter should be smooth and thick but pourable.
7. Pour the batter into the prepared cake pan and give it a couple of sharp raps against the counter to break up large air bubbles (this encourages an even crumb). Bake till the cake just starts to pull away from the sides of the pan and the center of the cake springs back when lightly pressed on top, 60 to 80 minutes. (Rotate at the 50 minute mark to check in with how it's progressing.)
8. Let the cake cool in the pan for 15 minutes, then invert onto a wire rack to cool completely. If your pan is retrofitted with a paper collar, remove the paper first and then turn the cake out.
9. Whilst the cake is cooling, get on with the frosting. Chuck the soft butter, salt, and vanilla extract into the bowl of a stand mixer fitted with a paddle attachment. Paddle the butter on a medium speed (#4 on a KitchenAid) till it’s fluffy and very pale, almost white.
10. Switch to the whisk attachment and, with the mixer on medium-high speed (#6 on KitchenAid), drizzle in the sweetened condensed milk in a slow but steady stream— this should take 4 to 5 minutes, which ensures the frosting doesn’t break. The frosting should look smooth and billowy. Add the chocolate-hazelnut spread and cocoa powder and whisk till fully incorporated and there are no dark streaks in the frosting. If your frosting looks soupy and grainy, don’t worry, it’s an easy fix! Just pop the entire bowl of frosting in the fridge for 20 to 30 minutes to firm up a little, then re-whip. It should come together beautifully.
11. Pile the frosting in giant clouds on top of the fully cooled cake. Chill the frosted cake for 30 minutes before serving.
12. The cake will keep, covered in an airtight container, in the refrigerator for up to 4 days. Let it sit at cool room temperature for 5 minutes before tucking in.