Erupting volcano

Erupting volcano

The Birthday Cake Book
Laura Edwards

Light the firework candle at the centre of this spectacular cake and await the applause.

For the cake


Quantity Ingredient
1 Marble cake
1 quantity chocolate buttercream, (see note)

For the honeycomb lava

Quantity Ingredient
200g golden syrup
350g caster sugar
2 tablespoons distilled white vinegar
2 teaspoons bicarbonate of soda

To decorate and assemble

Quantity Ingredient
200g granulated sugar
mint green food colour paste
3 tablespoons royal icing
30 cm round cake drum
200g milk chocolate, chopped
red or orange boiled sweets
4 packets popping candy
400g digestive biscuits, crushed
plastic dinosaurs
1 firework candle


  1. For the lava, line a 23 cm baking tray with baking parchment. Have a glass of cold water to hand. In a large, heavy-based pan, place the syrup, sugar, vinegar and 125 ml water. On a gentle heat, stir until the sugar dissolves. Increase the heat, bring to a boil and do not stir any more. If you have a sugar thermometer, boil it to 155°C. If not, drop a small ball of syrup into the glass of water. If it crackles and becomes a hard ball, it is ready. If not, boil until it is. Remove from the heat and add the bicarbonate of soda; it will erupt! Let it calm down, stir and pour into the prepared tray. Leave to set, then break into chunks. You won’t need it all for the cake. It keeps for a few days in a dry, airtight tin. Crush 100 g of it in a polythene bag with a rolling pin.
  2. For the grass, place the granulated sugar into a bowl. Mix a little green food colour with 2 teaspoons water in a bowl and pour into the sugar. Mix with your fingers and spread on a tray to dry. Mix every couple of hours. In a dry place, this keeps for weeks.
  3. Give the cakes a spell in the fridge to make them easier to shape. Trim all three so the tops are level. Cut each in half horizontally to give six cakes. Sandwich together with the buttercream. Stick a skewer into the top right through to the work surface, to use as a guide to avoid a lopsided volcano. Shape the cake from the top. Volcanoes do vary in shape; mine has a flat plateau on top and gently sloping edges. When you are happy, dig out a crater in which to place the candle.
  4. To assemble the cake, spread a thin layer of royal icing over the drum and press on the sugar ‘grass’. Remember, you won’t see the middle, so concentrate on the edges. Place the cake on to the drum.
  5. Melt the milk chocolate in a small bowl over simmering water, making sure the bowl does not touch the water. Cool slightly. Pour over the cake. Press on the crushed honeycomb and a few crushed boiled sweets for the embers, with the popping candy. Let the honeycomb tumble over the board. Surround the tableau with biscuit crumbs. Position the dinosaurs around and the firework candle in the crater.

For the buttercream

  • For the buttercream, melt 150 g of 55% cocoa solids chocolate in a bowl over simmering water; the bowl should not touch the water. Set aside to cool. Alternatively, use 2 tablespoons cocoa powder. Beat 225 g softened unsalted butter until really pale and fluffy, then add 300 g sifted icing sugar and 1 teaspoon vanilla extract. Beat for five minutes until light and creamy. Add the chocolate or cocoa powder and beat again.
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