Не то чтобы пюре было сложным, но без масла оно получается сухим.

Не то чтобы is an idiomatic softening phrase. It means something like:

it’s not exactly that... it’s not that... not that I’d say...

So Не то чтобы пюре было сложным does not mean a simple direct negation. It sounds more nuanced: the speaker is saying that difficulty is not really the issue.

This structure is often used when the speaker wants to reject one explanation and then give the real one:

Не то чтобы X, но Y
= It’s not so much that X; rather, Y

In this sentence, the idea is: The problem isn’t that mashed potatoes are difficult; the problem is that without butter they come out dry.

This is a very common point of confusion.

After не то чтобы, Russian often uses a past-tense form like было, even when the meaning is not actually about the past. It creates a kind of distance, similar to English not that it was/were... even when speaking generally.

So:

Не то чтобы пюре было сложным
sounds natural and idiomatic.

It does not necessarily mean that the mashed potatoes used to be complicated in the past. Instead, it is part of the standard pattern не то чтобы ... было ...

You can think of it as a set expression rather than a literal past-time statement.

Yes. Пюре is treated as a neuter singular noun in Russian.

That is why it agrees with:

• было — neuter singular past tense
• оно — the neuter pronoun it

So:

• пюре было
• оно получается

Even though пюре ends in -е, it is also an indeclinable noun, meaning its form usually does not change across cases. But grammatically, it still has gender and number, and here it behaves as neuter singular.

In this sentence, пюре is the subject, so it is in the nominative case.

Its form does not change because пюре is an indeclinable borrowed noun. That means the word keeps the same written form in different cases, even though its grammatical role still changes.

So in practice:

• nominative: пюре
• accusative: пюре
• genitive: often still пюре
• etc.

The case is understood from the sentence structure, not from a changed ending.

Here сложным is in the instrumental case, and that is very common after быть with a full adjective in predicate position.

So:

• пюре было сложным = the puree/mashed potatoes was difficult/complicated

Russian often uses the instrumental after verbs like быть, стать, оказаться, получаться when describing what something is, became, or turned out to be.

That is why you get:

• было сложным
• получается сухим

Could you ever see сложное? Yes, in some contexts nominative is possible, but сложным is the more standard and natural choice in this kind of sentence.

Because the preposition без always requires the genitive.

So:

• масло = nominative
• без масла = without butter

This is a fixed rule:

• без сахара = without sugar
• без воды = without water
• без масла = without butter

So масла is simply the genitive singular form of масло.

Here получается means something like:

comes out turns out ends up being

In cooking, this verb is extremely common. It is used for the result you get from making something:

• Суп получается вкусным = The soup comes out tasty
• Тесто получается слишком плотным = The dough turns out too dense

So оно получается сухим means that the mashed potatoes turn out dry.

The verb is получаться, the imperfective partner of получиться.

Here the imperfective is used because the sentence is talking about a general/habitual result, not one single completed occasion.

Not literally. In this verb, -ся is just part of the standard form получаться / получиться.

For learners, it is best to understand получаться as a complete vocabulary item meaning:

to turn out to come out to work out

So оно получается сухим should not be analyzed word-for-word as it obtains itself dry or anything like that. The reflexive ending is just part of how this verb is formed in Russian.

For the same reason as сложным: after verbs like получаться, Russian commonly uses the instrumental with a full adjective describing the result.

So:

• получается сухим
• получается вкусным
• получается слишком жидким

This is the normal pattern for saying something turns out a certain way.

Using сухое here would sound unnatural in standard Russian. The instrumental сухим is what you expect after получается.

No, they are different, and learners often mix them up.

Не то чтобы is the expression used here. It softens or qualifies what follows:

• Не то чтобы пюре было сложным...
  = It’s not exactly that mashed potatoes are difficult...

Не то что is a different construction and often appears in comparisons or emphatic contrasts, for example:

• Он не то что не помог — он всё испортил.
  = It’s not just that he didn’t help — he ruined everything.

So in your sentence, не то чтобы is the correct form.

Но means but, and it introduces the real point after the softened first clause.

The sentence has this structure:

Не то чтобы X, но Y

This is a very natural Russian pattern:

• first: reject or downplay one possible explanation
• then: give the actual issue

So here:

• X = the mashed potatoes are difficult
• Y = without butter, they turn out dry

That is why the sentence feels balanced and natural: the first part sets up a possible idea, and the second part corrects it.