Jednym z moich ulubionych składników jest szczypiorek, bo pasuje do jajek i twarogu.

It follows the pattern one of my favorite ingredients is chives.

A very literal breakdown is:

Jednym = one
z = of / from among
moich ulubionych składników = my favorite ingredients
jest = is
szczypiorek = chives

So the whole first clause means Chives is one of my favorite ingredients or more naturally One of my favorite ingredients is chives.

Because after jest in this kind of identifying/classifying sentence, Polish often uses the instrumental case.

The base form is jeden, but the instrumental singular is jednym.

So:

szczypiorek jest jednym z moich ulubionych składników
= chives is one of my favorite ingredients

This instrumental use is very common after być when saying what something is.

Here z means of / from among, not with.

The pattern is:

jeden z + genitive plural = one of ...

So:

z moich ulubionych składników
= of my favorite ingredients / from among my favorite ingredients

That is why all three words are in the genitive plural:

moich = genitive plural of mój
ulubionych = genitive plural of ulubiony
składników = genitive plural of składnik

They all agree with each other.

Because the idea is one of my favorite ingredients. You are choosing one item from a group of ingredients.

So Polish uses the plural:

składniki = ingredients
składników = of ingredients

If it were singular, it would mean something different.

Because szczypiorek is the noun being identified, and in this sentence it stays in the nominative form.

Even though the sentence begins with Jednym z moich ulubionych składników, the actual thing being talked about is szczypiorek.

You can also rearrange the sentence and see this more clearly:

Szczypiorek jest jednym z moich ulubionych składników.

That may make the grammar easier to notice.

Bo means because.

It is very common and natural in everyday Polish.

You could also say:

ponieważ = because, more formal or more careful
gdyż = because, more formal and more common in writing

So:

..., bo pasuje do jajek i twarogu.
is natural spoken-style Polish.

Because the understood subject is szczypiorek, which is singular.

So:

szczypiorek pasuje = chives goes well / chives suits

Even though jajek i twarogu refers to more than one thing, that is not the subject. They are just the things that chives goes well with.

If the subject were plural, then you would use pasują.

Pasować do can mean several related things:

• to suit
• to match
• to go well with
• to fit (for clothes or size)

In this food sentence, the best translation is goes well with.

So:

pasuje do jajek i twarogu
= goes well with eggs and twaróg

Also note that do requires the genitive case.

Because do takes the genitive.

So:

jajka becomes jajek
twaróg becomes twarogu

More specifically:

jajek = genitive plural of jajko
twarogu = genitive singular of twaróg

This is very typical after do.

Because they are being treated differently semantically.

jajka is a countable plural idea here: eggs.
twaróg is usually treated more like a mass noun: quark / curd cheese / farmer's cheese.

So Polish naturally says:

do jajek i twarogu

That is similar to English saying with eggs and cheese, not necessarily with eggs and cheeses.

Twaróg is a type of fresh white cheese common in Poland and nearby countries.

Possible English approximations are:

• quark
• farmer's cheese
• curd cheese

It is not exactly the same as typical American cottage cheese, although learners are sometimes shown that translation because it is somewhat similar.

Yes. Polish word order is flexible.

A very natural alternative is:

Szczypiorek jest jednym z moich ulubionych składników, bo pasuje do jajek i twarogu.

Both versions are correct. The difference is mostly emphasis:

• Jednym z moich ulubionych składników jest szczypiorek... emphasizes one of my favorite ingredients
• Szczypiorek jest jednym z moich ulubionych składników... starts directly with chives

Both sound natural.