Вечером в кафе мне захотелось не мороженого, а маленького пирожного.

Because this is an impersonal construction. Russian very often expresses cravings, sudden wishes, and physical or emotional states this way.

• мне = to me
• захотелось = it came to be wanted / I felt like

So мне захотелось is the natural Russian way to say something like:

• I felt like...
• I suddenly wanted...
• I had a craving for...

With food, this pattern is especially common and idiomatic.

Захотелось is the past-tense form of захотеться, a perfective verb meaning to start wanting, to suddenly feel like, or to get the urge for something.

It is related to:

• хотеть = to want
• хотеться = to feel like, to want in an impersonal way
• захотеться = to begin to feel like, to suddenly want

So мне захотелось suggests that the wish arose at that moment.

Because impersonal verbs in the past tense often appear in the default neuter singular form.

There is no normal grammatical subject here. Russian is not saying I wanted with я as the subject. Instead, it uses an impersonal structure, and the verb takes the neuter singular form:

• мне захотелось
• мне показалось
• мне не спалось

So захотелось is neuter singular because that is the standard form for this kind of impersonal sentence.

In this construction, the person experiencing the feeling is put in the dative case.

So:

• мне захотелось = I felt like / I wanted
• literally, something like to me it became wanted

This dative pattern is very common with impersonal verbs expressing states or feelings:

• мне холодно = I am cold
• мне грустно = I am sad
• мне хочется кофе = I feel like coffee

Because with food and drink, Russian often leaves that idea understood.

So мне захотелось мороженого naturally means:

• I felt like having some ice cream
• I wanted some ice cream

You do not need to add есть or съесть unless you want to emphasize the act of eating:

• мне захотелось съесть пирожное = I felt like eating a pastry

Without that extra verb, the sentence sounds very natural.

After хотеться / захотеться, the thing desired is very often put in the genitive, especially with food, drink, and indefinite cravings.

So:

• мне захотелось мороженого
• мне захотелось чаю
• мне захотелось сладкого

This gives a natural sense like:

• some ice cream
• some tea
• something sweet

In this sentence, the genitive sounds especially normal because the speaker is talking about what they felt like having, not about a specific clearly identified object.

Sometimes yes, especially in more colloquial speech or when a more specific item is meant. But in this sentence, the genitive is very natural and standard.

Compare:

• мне захотелось мороженого = I felt like some ice cream
• мне захотелось это мороженое = I wanted this ice cream

So the genitive often gives a less specific, more craving-like feeling. With desserts, drinks, and snacks, that is very common.

Because the adjective has to agree with the noun in case, number, and gender.

Since пирожного is genitive singular, маленького must also be genitive singular.

Dictionary forms:

• маленькое пирожное

In this sentence:

• маленького пирожного

So the adjective changes because the noun changes.

Because historically they are adjectives used as nouns. This is called substantivization.

That is why their forms look adjectival:

• мороженое → genitive мороженого
• пирожное → genitive пирожного

In modern Russian, learners can treat them as ordinary neuter nouns in meaning, but it is useful to know that they still decline like adjectives.

Because не X, а Y is the normal Russian pattern for not X, but Y instead.

So:

• не мороженого, а маленького пирожного

means that the speaker is correcting or replacing one option with another:

• not ice cream, but a small pastry

Russian usually uses а in this kind of correction. Но is more for general contrast, not this specific replacement pattern.

Вечером is the instrumental singular of вечер, used adverbially to mean in the evening.

This is a very common time expression in Russian:

• утром = in the morning
• днём = during the day
• вечером = in the evening
• ночью = at night

So Russian often uses a bare case form here instead of a preposition.

В кафе means in the café or at the café.

The preposition в with location normally goes with the prepositional case, but кафе is an indeclinable noun, so its form stays the same.

That means кафе looks the same in different case roles:

• кафе
• в кафе
• из кафе

This is common with some loanwords in Russian.

The difference is aspect.

• хотелось = imperfective, describes a state or ongoing desire
• захотелось = perfective, shows the desire arising at a particular moment

So:

• мне хотелось мороженого = I wanted some ice cream / I was in the mood for ice cream
• мне захотелось мороженого = I suddenly felt like some ice cream

In this sentence, захотелось fits well because the speaker is describing what they ended up wanting in that situation.

Yes. Russian word order is flexible, and changes mainly affect focus and emphasis, not basic meaning.

This order:

• Вечером в кафе мне захотелось не мороженого, а маленького пирожного

puts the scene first:

• Вечером = time
• в кафе = place

Then it gives the experiencer and the feeling:

• мне захотелось

And finally the important contrast:

• не мороженого, а маленького пирожного

That makes the ending feel especially prominent. Russian often places the most informative or contrastive part later in the sentence.