Для теста нужен литр молока, а для крема — всего двести граммов сахара.

Because both follow the preposition для, and для always requires the genitive case.

• тесто → теста
• крем → крема

So:

• для теста = for the dough / for the batter
• для крема = for the cream / for the filling

These are singular genitive forms, not plurals.

No. This is a very common false friend.

• тесто = dough / batter
• тест = test / exam

So для теста in a cooking context means for the dough or for the batter, not for the test.

Нужен means needed or required.

Grammatically, it is the short form of the adjective нужный. In Russian, short-form adjectives are often used like predicates:

• нужен = needed (masculine singular)
• нужна = needed (feminine singular)
• нужно = needed (neuter singular)
• нужны = needed (plural)

So Для теста нужен литр молока is literally something like:

For the dough, a liter of milk is needed.

Russian also usually omits the present-tense verb to be, so there is no separate word for is here.

Because нужен agrees with литр, which is a masculine singular noun.

The important word is the main noun of the phrase:

• литр = masculine singular
• молока just tells you of what

So:

• нужен литр молока
• not нужно литр молока

Compare:

• нужна чашка воды = a cup of water is needed
• нужно молоко = milk is needed
• нужны яйца = eggs are needed

Because Russian normally uses the genitive after words of quantity or measure.

Here you have:

• литр молока = a liter of milk
• двести граммов сахара = two hundred grams of sugar

This is very common with food and materials:

• стакан воды = a glass of water
• килограмм муки = a kilogram of flour
• ложка масла = a spoonful of butter/oil

So молока and сахара are in the genitive because they follow measurement words.

Because двести requires the noun after it to be in the genitive plural.

So:

• два грамма
• пять граммов
• двести граммов

This is part of the Russian numeral system, which has several different patterns.

A useful comparison:

• двести граммов = 200 grams
• двести два грамма = 202 grams
• двести пять граммов = 205 grams

So the ending changes depending on the numeral pattern.

The dash shows that something has been left out because it is easy to understand from the first clause.

The full version would be something like:

а для крема нужно всего двести граммов сахара

Russian often omits repeated words in parallel structures, especially in written style. The dash helps mark that omission.

So the second part means:

and for the cream, only 200 grams of sugar

with нужно understood.

Here всего means only, just, or as little as.

It adds the idea that the amount is small or not very much:

• всего двести граммов сахара = only 200 grams of sugar

So the sentence is not just giving a quantity; it is also slightly emphasizing that the cream needs just 200 grams.

Because а often connects two things that are being compared or contrasted, even if the contrast is mild.

Here the sentence compares two recipe parts:

• for the dough: one liter of milk
• for the cream: only 200 grams of sugar

So а works well because it sets up a parallel contrast:

for the dough ..., whereas for the cream ...

If you used и, it would sound more like simple addition, with less of that comparison.

This word order puts the purpose/topic first.

In a recipe, this is very natural. The sentence is organized by parts of the dish:

• Для теста ...
• для крема ...

That is similar to English recipe style:

• For the dough, ...
• for the cream, ...

So the sentence is structured around what each ingredient is for, not just around the ingredients themselves.

Yes. A full version would be perfectly correct:

Для теста нужен литр молока, а для крема нужно всего двести граммов сахара.

That version is a little more explicit. The version with the dash is simply more compact and stylistically neat.

Both are natural, but the dash version is especially common when Russian avoids repeating the same idea twice.

You could, but it is a slightly different way of expressing the idea.

• Для теста нужен литр молока = a liter of milk is needed for making the dough
• Тесту нужен литр молока = the dough needs a liter of milk

The second version is understandable, but in recipe language для + genitive is usually the more natural and standard way to label ingredients by purpose.

So in a cooking context, для теста sounds especially appropriate.