Moist one-bowl chocolate cake

This is the cake I make when it's someone's birthday and I haven't had time for anything else. Twenty minutes' work, one bowl and a result that looks like it came from a cake shop.

The first time I made it, I thought I'd got the quantities wrong. When the hot water went in, the batter turned as runny as chocolate soup and I very nearly threw it away. I didn't, and out came the moistest cake I'd tasted in years.

Ever since, it's the one we make most at home. No softened butter, no whisking eggs. You weigh, sift, mix for a couple of minutes and the oven does the rest.

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Why it's so moist

The hot liquid. Hot water or freshly brewed coffee blooms the cocoa and brings out all its flavour. It also gives a very loose batter that bakes into a moist, tender crumb.

The yoghurt. It brings the acidity the bicarbonate of soda needs to make the cake rise, plus moisture that lasts for days.

Oil instead of butter. Oil stays liquid at room temperature, so the cake is just as tender the next day. Butter firms up as it cools and hardens the crumb.

The recipe: Moist one-bowl chocolate cake

• Prep: 20 minutes
• Baking: 50 to 60 minutes
• Rest before turning out: 10 minutes
• Serves: 12 to 14
• Tin: 2.5 litres (Clásico or Bloom)

Ingredients

Dry ingredients

• 260 g plain flour (2 cups)
• 400 g caster sugar (2 cups)
• 85 g unsweetened cocoa powder (1 cup)
• 10 g bicarbonate of soda (2 tsp)
• 4 g baking powder (1 tsp)
• 5 g fine salt (1 level tsp)

Wet ingredients

• 240 g plain unsweetened Greek yoghurt (or 240 ml buttermilk, see notes)
• 120 ml sunflower or corn oil (½ cup)
• 2 large eggs, lightly beaten
• 5 ml vanilla extract (1 tsp)
• 240 ml very hot water or freshly brewed coffee (1 cup)

For the tin

• Softened butter
• 1 tbsp cocoa powder

Method

1. Get the oven and tin ready. Preheat to 175 °C, top and bottom heat, no fan. Brush the whole inside of the tin with softened butter, working it into every groove and around the central tube. Add the tablespoon of cocoa, turn the tin so it coats everything and tap out the excess upside down. With cocoa instead of flour, you won't get a white film on the cake.
2. Sift the dry ingredients. Sift the flour, sugar, cocoa, bicarbonate of soda, baking powder and salt into the bowl of your stand mixer. Give them a few turns with a hand whisk so they're well mixed and aerated.
3. Add the wet ingredients. With the mixer on low, add the yoghurt, oil, eggs and vanilla, in that order. Turn up to medium-low and mix for 1 to 2 minutes, until the batter is smooth and lump-free.
4. The hot liquid. Turn the mixer down to its lowest speed and pour in the hot water or coffee in a thin, steady stream. The batter will be very runny, almost like soup. That's normal, and it's exactly what you want.
5. Bake. Pour the batter carefully into the tin and bake at 175 °C for 50 to 60 minutes. From 50 minutes, push a skewer into the highest, most central part: it's ready when it comes out clean or with a couple of dry crumbs.
6. Ten minutes, then turn it out. Leave the tin on a wire rack for exactly 10 minutes, with a timer. Put the rack or a plate on top, hold them together, flip in one go and lift the tin straight up. The crumb is very tender: let it cool completely before slicing.

Notes and tips

Water or coffee? Coffee won't make the cake taste of coffee. It boosts the chocolate and makes it deeper and darker. If there are children at home, use decaf.

Buttermilk instead of yoghurt. Put 1 tablespoon of lemon juice or white vinegar in a measuring jug and top up with whole milk to 240 ml. Stir, wait 10 minutes for the milk to curdle and thicken slightly, and use it in place of the yoghurt.

Everything at room temperature. Yoghurt and eggs straight from the fridge cool the batter and lengthen the baking time. Take them out half an hour before.

A brush beats spray. Cake release spray doesn't reach the bottom of the pattern properly and, over time, leaves a sticky film on the non-stick coating. We explain it in our guide to turning out a cake without it breaking.

If you want to cover it. Heat 100 ml double cream and pour it over 100 g chopped dark chocolate. Wait a minute, stir until glossy and pour it over the cooled cake.

Storage

• It stays tender for 4 to 5 days at room temperature, in an airtight container or under a cake dome.
• Don't keep it in the fridge: the crumb dries out and loses flavour. If you've covered it in chocolate and it's very hot, then yes, but take it out half an hour before serving.
• To freeze, cut it into slices, wrap them in cling film and keep for up to 3 months. Defrost at room temperature without unwrapping.

Which tin to use

This recipe is designed for a 2.5-litre tin. I make it in the Clásico and the Bloom, where the petals come out beautifully defined. It turns out just as well in the rest of our 2.5-litre moulds: Flow, Blaze, Plait, Twist, Gleam, Flare and Vortex.

In a smaller tin, only if you adjust the quantities. Made as written, the recipe would overflow the 2-litre Cascada and Amour and the 1.8-litre Espiral. To use them, multiply every ingredient by 0.8 for the 2-litre moulds and by 0.7 for the 1.8-litre one. Beat the eggs and weigh them: a large egg is about 55 grams out of its shell. And start checking the bake about 10 minutes earlier.

The rule that never fails, whatever the tin, is not to overfill it. In our guide to tin capacities and conversions you'll find the volume of each one and how to convert any recipe.

What I used

• The Bloom mould or the Clásico mould, both 2.5 litres, in cast aluminium with a double non-stick coating.
• The set of baking trays with rack. The rack is where the cake spends its ten minutes before turning out, and where it cools afterwards, with air circulating underneath.
• An olive wood board or a teak board to bring it to the table and slice it in front of everyone.
• A pastry brush. If your tin has a few years behind it, have a look at how to look after the non-stick coating so it keeps releasing like the first day.

Frequently asked questions

Why is the chocolate cake batter so runny? Because of the hot water or coffee added at the end. It's the key to the recipe: it hydrates the cocoa and gives a very moist crumb. Don't add flour to thicken it.

Does the cake taste of coffee if I use coffee instead of water? No. Coffee just intensifies the chocolate flavour and nobody will notice it's there. If you'd rather avoid caffeine, use decaf.

Can I replace the Greek yoghurt? Yes, with the same amount of buttermilk, homemade or shop-bought. Ordinary plain yoghurt works too, although the crumb comes out slightly less dense.

Can you freeze chocolate cake? Yes. Cut into slices and well wrapped in cling film, it keeps for up to 3 months in the freezer. Defrost at room temperature without unwrapping.

Can I make it in a 2-litre tin? Only if you adjust the quantities: multiply every ingredient by 0.8 and start checking about 10 minutes earlier. With the full recipe, a 2-litre tin will overflow.

How long should I wait before turning it out? Ten minutes from when it comes out of the oven. Any sooner and the crumb can't hold together and breaks. Much later and the fat cools, sticks to the tin and the cake is harder to release.