This majestic French confection, originally called croque en bouche ("crunch in the mouth"), is the centrepiece at celebrations, many of them weddings. A tower of cream puffs built around a cone-shaped mould and held together with caramel, which adds the essential crunch, it's attributed to Antonin Carême, the 19th-century chef famed for the architecture he brought to buffet tables.
Three cooking skills are key here: a mastery of choux pastry, crème pâtissière (or pastry cream), and sugar cooking. For the pastry, water and milk are brought to the boil along with butter and salt so the butter emulsifies in the liquid. Have the sieved flour on a sheet of baking paper ready to shoot into the liquid all at once and, critically, off the heat. Beat the dough until it forms a ball, which will look a bit wet, then return to low heat and beat it until it leaves the sides of the pan. I turn the dough out into a bowl to cool slightly before adding the beaten eggs; do this in several quantities, beating well until smooth before adding more. Watch for the "dropping" test; the dough should fall slowly off the spoon, and once this consistency is reached add no more egg. The buns are baked until they're quite dry, reducing the temperature so they don't get too dark.
Crème pâtissière contains starch, which prevents the egg yolks from curdling, so it's almost foolproof. Don't combine the yolks with the sugar in advance - it "cooks" the eggs, which makes for a thinner texture. I add half the sugar to the milk, so you need to take care that it dissolves before the milk boils. Whisk the hot milk thoroughly into the egg and sugar mixture with a wooden spoon, going right into the corners of the pot, then change to a whisk. Once the mixture is very thick and smooth, tip it into a bowl over another bowl containing a slurry of ice, salt and water, and stir it with the whisk so it cools quickly - the quicker it cools, the fresher the flavour.
The pastry cream may be made up to two days ahead, provided it's refrigerated with a sheet of plastic wrap pressed tightly over the surface and the bowl is sealed. When needed, simply beat it well with a whisk - a mixer would cause the pastry cream to break down. And as long as the pastry cream is really thick, a little liqueur may be added, and finely ground praline makes a welcome variation.
The trickiest part is cooking sugar to the "crack" stage for the caramel. An untinned copper pan is ideal - copper is a good heat conductor. A sugar thermometer is essential to get it exactly at 160C; beyond that and it's hard to coat the buns with the syrup. I make three lots - the first two to dip the buns in, and the last to glue them together. Use a fork or metal skewer to quickly dip the tops of the choux buns into the hot caramel, let the excess run off, then place them on a tray dipped-side up.
To fill the buns, pierce their bases with a paring knife, then pipe in the pastry cream. Once this is done, start the last batch of sugar. When it's ready, start dipping and sticking the buns to the mould, first around the base, then upwards in a spiral, working quickly before the sugar in the pan cools - an extra set of hands helps. Stick on decorative elements, such as sugared almonds or candied violets, as you go. Let the croquembouche stand for the sugar to set and harden, then carefully tip it on its side so it rests on one of your hands and gently twist the mould to remove it, then place the croquembouche on a serving platter.
In a lovely tradition, croquembouches are often served by being struck with a silver hammer to scatter the buns across the table for all to eat in the spirit of celebration. So get cracking for your next party.