Chocolate sponge cake

Mixing the cocoa powder with boiling water is a process called blooming. It intensifies the flavour of the cocoa powder giving a really chocolatey flavour.

Mary uses the all-in-one method for her cakes. It helps to have very soft butter (or margarine that's suitable for baking) so that you don't overbeat the mixture. Overbeating could result in a tougher cake texture. To soften your butter, cut into small cubes, spread onto a plate, cover lightly with kitchen paper and leave at room temperature for at least 30 minutes (or watch the How-to video below).

Mary's preference for dark chocolate is to use varieties with 40–50 percent cocoa solids. A higher amount of cocoa solids will still work well but makes a deeper, less sweet cake. Whatever you use, make sure you chop it into small even pieces (you could even grate it).

The name sandwich tin is a little confusing as they aren’t anything to do with bread-based sandwiches but are designed for baking round sponge cakes that you ‘sandwich’ together with a filling. It’s worth treating yourself to a set of loose-based sandwich tins with straight vertical sides rather than tapering side produce a better-looking cake that’s also easier to ice. The loose base makes it easier to lift the sponge out.

A rounded teaspoon is a measure of a dry ingredient, such baking powder or a spice, that’s been scooped into a teaspoon leaving a few millimetres rising above the rim of the spoon, rather than a ‘level’ teaspoon where a knife has been taken across the rim to give a flat surface. It’s a useful measure for recipe when a little more than a teaspoon of an ingredient is called for and is roughly equal to 1¼ tsp.

Golden caster sugar is made using unrefined sugar. It’s a pale sandy colour and gives a mild caramel-like flavour to bakes. White caster sugar can be substituted but, if you want a richer flavour, try mixing a little soft light brown sugar with caster sugar.

To help make your sponges evenly sized for a more professional finish, weigh the cake batter in the tins to make sure they are the same before you bake them.

Chocolate ganache makes a super-simple icing for chocolate cakes and looks really impressive. You’ll need to leave it to cool for up to an hour before it’s ready to use. It should be soft, creamy and easily spreadable, but if it’s too soft it will run down the sides of the sponges. It's also crucial the cakes are completely cold before icing, as any residual heat could melt the ganache.

If you don’t have apricot jam, you can use seedless raspberry instead. Or push any raspberry or strawberry jam through a sieve to remove the seeds, adding an extra tablespoon to make up for any loss. The jam isn’t essential to the cake, although it helps balance the flavour of the super-rich chocolate ganache, so feel free to skip it if you prefer.

To make an orange-flavoured chocolate cake, add the finely grated zest of one orange to the cake batter and spread the cake with fine shred marmalade instead of apricot jam.

How to freeze

The sponges for this cake can be frozen ahead if you like. Allow them to cool completely, then place each one on a circle of baking paper and cover with another circle of baking paper – this will help prevent the sponge sticking – before wrapping tightly in two layers of kitchen foil. Label and freeze for up to 1 month.

To thaw, unwrap and place the frozen cakes a wire rack, loosely covered with foil. Leave at room temperature for about an hour before icing.