Bird’s Milk Cake in London: What Ptichye Moloko Is

Bird’s Milk is the cake that makes people who have never eaten it ask what it is twice, because the first answer never lands. It is a thick layer of pale, aerated soufflé sitting on a thin sponge, sealed under dark chocolate. It is not mousse, because mousse is set with cream and collapses. It is not marshmallow, though it is closer to marshmallow than to anything else. And it is not a cheesecake, whatever the texture suggests at first.

The name is an old Russian idiom. Ptichye moloko, bird's milk, is the thing that does not exist, the impossible luxury, what you promise somebody when you mean you would get them anything at all. Attaching that to a cake was a piece of naming so good that it survived the state that invented it.

The one cake with a patent

Most Soviet cakes were factory recipes that spread by imitation. This one is unusual: it was developed in the 1960s and 1970s, refined at the Praga restaurant in Moscow under the confectioner Vladimir Guralnik, and in 1982 it became the first confectionery product in the USSR to be granted a patent.

That mattered because the thing being protected was not a flavour but a technique. The problem Guralnik solved was how to make a soufflé that would hold its shape at room temperature, survive being cut, and still eat as though it were about to disappear. Gelatine would not do it. Gelatine sets soft, melts at body heat, and gives a wobble that is wrong for this cake.

Agar is the whole answer

The setting agent is agar, which comes from seaweed rather than from animal collagen, and it behaves in a way gelatine cannot.

Agar has to be boiled to activate, well above the temperature gelatine would be destroyed at. It sets at a much higher temperature than gelatine, around forty degrees rather than around fifteen, and once set it stays set until it is heated to something close to boiling again. That is why a slice of Bird’s Milk can sit on a plate in a warm room and keep its edge, and why the texture is clean and yielding rather than wobbling.

The working sequence is unforgiving. Sugar syrup and agar are boiled together to a precise temperature, then poured in a thin stream into whipped egg whites while they are still beating, then softened butter and condensed milk are worked in, and all of this has to happen before the agar reaches its setting point. Once it starts to set, it is set. There is no gentle folding stage, no pause to answer the door. A batch that sets in the bowl is a batch that gets thrown away.

The sponge and the chocolate

Under the soufflé there is a thin layer of sponge, and its job is structural rather than decorative: it gives the soufflé something to sit on and gives the slice a base that a server can lift.

Over the top goes dark chocolate, poured thin and left to set. It has two jobs. It seals the soufflé so it does not dry at the surface, and it provides the one bitter note in a cake that is otherwise entirely sweet and entirely soft. Cut a slice and the chocolate cracks under the knife before the soufflé gives way, and that small resistance at the top is part of what the cake is.

Bird's Milk CakeBird’s Milk cake, ptichye moloko, 18 cm. Airy soufflé over sponge under dark Belgian chocolate.from £78Order this

What a bad one is like

There are two common failures and both are about the set.

Too much agar, or agar boiled too hard, gives a soufflé that is rubbery. It bounces. You can lift a slice by one corner and it holds its shape like a piece of jelly, which is impressive and horrible.

Too little, or agar added off the boil so it never activated, gives something that slumps on the plate within a few minutes and reads as a slightly stiff mousse. It tastes fine and it is not the cake.

The third failure is not technical. It is sweetness with nothing against it, which happens when the chocolate on top is milk chocolate or is spread too thin. The bitterness matters.

Who it suits

This is the cake for a table that cannot agree. It is light enough that somebody who says they do not eat dessert will finish a slice, it is not floury, it has no nuts in it, and it is mild enough for children while still being interesting to somebody who eats a great deal of cake.

It is also the cake we would suggest for a warm room and a long evening, because agar does not mind waiting in a way that cream does.

For a larger table, it is one of the three we make in a tray size for events rather than only at 18 cm, and those are arranged by talking to us rather than through the checkout.

Prague Cake (18cm)£82Cake “Charodeyka”£61

Why a good one is hard to buy

Bird’s Milk is the cake most often sold badly in London, and the reason is agar.

Agar behaves nothing like gelatine and a kitchen that has not worked with it produces one of the two failures described above on the first several attempts. It also gives no second chances: once the mixture starts to set in the bowl, it is scrap. A commercial kitchen weighing up whether to carry this cake is looking at a real waste rate while somebody learns it.

So most versions sold here take the easy route and set the soufflé with gelatine, which gives a wobble and a slower, waxier melt, or with a stabilised whipped cream, which is really a mousse cake wearing the name.

There is a quick test if you are buying one. Leave a slice on a plate at room temperature for twenty minutes. A proper agar set will stand there with its edges sharp. Gelatine will start to soften and lean. Nothing else in the cake tells you as much as that does.

Ours is made with agar, boiled and worked in the traditional sequence, because the texture it gives is the entire reason the cake was worth patenting.

Common questions

What does Bird’s Milk cake taste like?

Vanilla and condensed milk, with a clean dairy sweetness and a bitter edge from the dark chocolate on top. The flavour is mild. The texture is the point: a dense foam that dissolves rather than chews.

Is it gluten free?

No. The thin sponge base contains wheat flour. The soufflé itself contains no flour, but the cake as a whole is not suitable for a coeliac. The Esterházy cake is our gluten free option and is made without flour at all.

Is it suitable for vegetarians?

The setting agent is agar, which is seaweed rather than gelatine, so there is no animal collagen in it. It does contain eggs and milk, and it contains soya through the chocolate.

How long does it keep?

Three days in the fridge, boxed, and it is at its best on the first two. Take it out of the fridge about twenty minutes before serving. Unlike most of our cakes it will sit happily on a table for a couple of hours without losing its shape.

How many people does it serve?

The 18 cm cake gives ten to twelve slices. It is lighter than the honey cake or the Napoleon, so people do tend to accept a second slice, which is worth knowing when you are counting.

Ordering one

Bird’s Milk is made to order in Belgravia and delivered across London and Surrey. Forty eight hours notice, £12 delivery in central London and £15 elsewhere, £50 minimum order. Choose the date at checkout and it is made for that date.