Белые грибы засушим, разве что часть будем солить.

No. Белые грибы is the normal Russian name for porcini / cep / king bolete mushrooms.

Literally it means white mushrooms, but as a set expression it usually refers to that specific mushroom, not to mushrooms that simply happen to be white.

Because here the phrase is the direct object of засушим.

With inanimate plural nouns, Russian uses the same form for nominative and accusative. So:

• nominative: белые грибы
• accusative: белые грибы

That is why the sentence uses белые грибы.

You would see белых грибов in the genitive, for example:

• нет белых грибов = there are no porcini mushrooms
• много белых грибов = many porcini mushrooms

Засушим is the 1st person plural perfective future of засушить.

It means something like:

• we’ll dry them
• we’ll dry them for storage
• we’ll dry them thoroughly

With food, засушить often suggests preserving something by drying it.

This is different from сушить, which is imperfective and describes the process more generally. Compare:

• будем сушить = we’ll be drying / we’ll dry
• засушим = we’ll dry them up / we’ll get them dried

So засушим sounds more result-focused.

This is mainly an aspect difference.

• засушим is perfective: it presents drying as a finished result.
• будем солить is imperfective future: it presents salting as an activity or method, not as a sharply bounded completed result.

That fits the meaning well: the main plan is to dry the mushrooms, and salting is only a possible exception for some of them.

A speaker could also say часть засолим, which would sound more result-oriented: we’ll salt-preserve some of them. But будем солить is perfectly natural here.

Разве что is an idiomatic expression meaning something like:

• except maybe
• unless perhaps
• at most
• with the possible exception that

In this sentence it introduces a small exception to the main plan:

• Белые грибы засушим = we’ll dry the porcini mushrooms
• разве что часть будем солить = except maybe we’ll salt some of them

So the overall feeling is: We’ll dry them—though we might salt some of them instead.

Here it means to preserve by salting / brining.

In Russian, солить can mean either:

• to salt in the ordinary sense, or
• to preserve in salt/brine

With mushrooms, the preservation meaning is very natural. So this is not about sprinkling salt on food before eating it.

Yes, a little is omitted.

Часть means part or a portion, and here it really means:

• часть из них = part of them
• some of them

Russian often leaves из них unspoken when it is obvious from context. So:

• часть будем солить

naturally means:

• we’ll salt some of them

Russian word order is flexible, and this placement highlights часть.

By saying:

• разве что часть будем солить

the speaker emphasizes that it is only some of the mushrooms that will be salted.

A different order, such as будем солить часть, is also possible, but the original word order makes the contrast clearer after разве что.

Because разве что часть будем солить is an added exception or afterthought to the main clause Белые грибы засушим.

The comma marks that break:

• main statement: Белые грибы засушим
• qualification/exception: разве что часть будем солить

In speech, you would usually hear a pause there too.