Jeśli chodzi o deser, najbardziej lubię sernik.

Here Jeśli chodzi o is an idiomatic expression meaning as for, when it comes to, or speaking of.

So:

• Jeśli chodzi o deser = As for dessert / When it comes to dessert

It is very common in Polish when you want to introduce a topic and then comment on it.

Examples:

• Jeśli chodzi o muzykę, lubię jazz. = As for music, I like jazz.
• Jeśli chodzi o pracę, wszystko jest w porządku. = As for work, everything is fine.

By itself, jeśli usually does mean if. But in the fixed phrase jeśli chodzi o, it does not work like a normal conditional if sentence.

So this is best learned as a whole expression:

• jeśli chodzi o... = as for... / when it comes to...

You should not translate it word for word. Literally, chodzi o means something like it is about / it concerns, but the whole phrase functions as a topic-introducer.

The preposition o in the expression chodzi o takes the accusative case.

So:

• chodzi o deser = it is about dessert

The noun deser is masculine inanimate, and in the singular its accusative form is the same as its nominative form:

• nominative: deser
• accusative: deser

So even though the case changes grammatically, the form looks the same.

Compare with another noun where the form changes:

• chodzi o kawę = it is about coffee

Here you can see the accusative more clearly.

Because Jeśli chodzi o deser is an introductory phrase at the beginning of the sentence.

Polish often separates this kind of opening phrase with a comma:

• Jeśli chodzi o deser, najbardziej lubię sernik.

This is similar to English punctuation in sentences like:

• As for dessert, I like cheesecake most.

So the comma helps mark the topic before the main statement.

Najbardziej means the most.

It comes from:

• bardzo = very
• bardziej = more
• najbardziej = most

So:

• lubię = I like
• najbardziej lubię sernik = I like cheesecake the most

It is used with verbs to show the highest degree of preference, intensity, or liking.

Examples:

• Najbardziej lubię lato. = I like summer the most.
• Najbardziej boję się pająków. = I am most afraid of spiders.

That is a very common learner question.

• najbardziej is usually used for degree/intensity: liking something more than anything else
• najwięcej is usually used for quantity/amount

So in this sentence, the idea is which dessert do I like most?, not which dessert do I consume in the greatest quantity?

Correct:

• Najbardziej lubię sernik. = I like cheesecake the most.

Different meaning:

• Najwięcej jem sernika. = I eat the most cheesecake.

So najbardziej fits preference, while najwięcej fits amount.

Yes, Polish word order is quite flexible.

The neutral order here is:

• najbardziej lubię sernik

But you could also hear:

• Lubię najbardziej sernik
• Sernik lubię najbardziej

These all mean roughly the same thing, but the emphasis changes.

• Najbardziej lubię sernik sounds natural and neutral.
• Sernik lubię najbardziej puts extra focus on sernik.
• Lubię najbardziej sernik is possible, but often sounds a bit less natural than the first version.

Polish often moves words around for emphasis, because case endings do a lot of the grammatical work that word order does in English.

Lubię is the 1st person singular present tense form of lubić, which means to like.

Conjugation of lubić:

• ja lubię = I like
• ty lubisz = you like
• on/ona/ono lubi = he/she/it likes
• my lubimy = we like
• wy lubicie = you all like
• oni/one lubią = they like

So in the sentence:

• najbardziej lubię sernik = I like cheesecake the most

The -ę ending tells you it is I.

Polish has no articles, so there is no direct equivalent of a, an, or the.

That means sernik can mean:

• cheesecake
• a cheesecake
• the cheesecake

The exact meaning depends on context.

In this sentence, English naturally uses the general meaning:

• I like cheesecake the most

So if you are an English speaker, it is important not to expect a Polish article before nouns.

The sentence with singular deser is understandable and correct:

• Jeśli chodzi o deser, najbardziej lubię sernik.

But many speakers would also say, and perhaps more naturally:

• Jeśli chodzi o desery, najbardziej lubię sernik. = When it comes to desserts, I like cheesecake the most.

Why? Because in English and Polish alike, when talking about a category of foods, the plural often sounds more natural.

So:

• deser = dessert, as a general category
• desery = desserts, kinds of desserts

Both are possible, but desery may sound a little more idiomatic in everyday conversation.

Yes. This sentence is good Polish, but there are several natural alternatives depending on style.

Some common ones:

• Najbardziej lubię sernik na deser. = I like cheesecake best for dessert.
• Jeśli chodzi o desery, najbardziej lubię sernik.
• Moim ulubionym deserem jest sernik. = My favorite dessert is cheesecake.
• Sernik lubię najbardziej. = Cheesecake is what I like the most.

They all express similar meaning, but with slightly different emphasis:

• Jeśli chodzi o... sounds like you are introducing a topic
• Moim ulubionym deserem jest... sounds a bit more direct and declarative
• Sernik lubię najbardziej emphasizes sernik

A rough English-friendly pronunciation would be:

• YEH-shlee HOD-jee o DEH-sehr, nay-BAR-djye loo-BYEH SEHR-neek

A few useful notes:

• jeśli: je sounds like ye
• ch in chodzi is like a strong h
• dz in chodzi sounds a bit like דזש in English, but softer
• lubię ends with a nasal vowel ę, though in normal speech it is often pronounced somewhat like -eh or -em depending on context
• stress in Polish usually falls on the second-to-last syllable

So the stressed syllables are roughly:

• JEŚ-li
• CHO-dzi
• DE-ser
• naj-BAR-dziej
• LU-bię
• SER-nik