Stamattina il panettiere mi ha tenuto da parte due panini, perché sapeva che arrivavo tardi.

Stamattina means this morning and is very common in everyday Italian.

It is essentially the same idea as questa mattina, but:

• stamattina is shorter and very natural in speech
• questa mattina is a little fuller and slightly more explicit

So these are both normal:

• Stamattina il panettiere...
• Questa mattina il panettiere...

There is no important meaning difference here.

Italian often uses the definite article where English might not.

Here, il panettiere means the baker: the specific baker the speaker has in mind, probably the usual one from the local bakery.

Without the article, panettiere would generally not work in this sentence. Italian normally wants the article with a noun used this way:

• il panettiere
• il dottore
• la vicina

So il panettiere is simply the normal way to say the baker.

This is a very useful expression.

Tenere da parte means:

• to keep aside
• to set aside
• to reserve

So mi ha tenuto da parte due panini means that the baker kept two rolls aside for the speaker, so that nobody else would buy them.

Literally, it is something like:

• he kept aside for me two rolls

But in natural English it is better understood as:

• he set aside two rolls for me
• he saved two rolls for me

Here mi is an indirect object pronoun, meaning something like for me / to me, depending on the verb.

With tenere da parte in this context, Italian commonly uses the indirect pronoun:

• mi ha tenuto da parte due panini
• ti ha tenuto da parte il giornale
• ci hanno tenuto da parte un tavolo

Using per me is possible in some rephrasings, but it is less direct and less idiomatic in this exact structure.

A very natural alternative would be:

• ha tenuto da parte due panini per me

But in the original sentence, mi ha tenuto da parte is perfectly normal and very common.

Yes. The verb is tenere and its past participle is tenuto.

So:

• infinitive: tenere
• passato prossimo: ha tenuto

It is irregular in the sense that you do not form the participle as tenito. You have to learn tenuto.

A few examples:

• Ho tenuto il posto per te.
• Mi hanno tenuto da parte una copia.
• Hai tenuto tutto?

This is a classic contrast in Italian.

• ha tenuto is passato prossimo, used for the main completed action
• sapeva and arrivavo are imperfetto, used for background information or an ongoing situation

So the sentence is structured like this:

• the baker set aside the rolls → main event
• he knew something → background reason
• I was arriving / would be arriving late → situation he knew about

In other words:

• ha tenuto tells us what happened
• sapeva che arrivavo tardi explains why

Also, sapeva is especially important here. Compare:

• sapeva = he knew
• ha saputo often means he found out / he learned

So sapeva is the right tense if the idea is that he already knew.

Both can be possible in Italian, but they give slightly different feels.

In this sentence, arrivavo tardi is very natural. The imperfect can be used to express something that was expected or viewed as part of the situation at that time:

• sapeva che arrivavo tardi = he knew I was going to arrive late / he knew I’d be late

If you say sapeva che sarei arrivato tardi, that is also possible, but it sounds a bit more explicitly like he knew that I would arrive late.

So:

• arrivavo tardi = very natural, narrative, tied to the situation
• sarei arrivato tardi = more clearly future-in-the-past

The original sentence sounds very idiomatic and everyday.

Here che means that.

It introduces a clause after sapeva:

• sapeva che arrivavo tardi
• he knew that I was arriving late

In English, that is often optional:

• he knew I was late
• he knew that I was late

In Italian, che is normally kept. You would not usually leave it out here.

After a number, Italian usually uses the noun directly:

• due panini
• tre libri
• quattro amici

So due panini simply means two rolls / two sandwiches, depending on context.

You would add an article only if you meant some specific, already identified ones:

• i due panini = the two rolls
• quei due panini = those two rolls

But here the sentence is just giving the quantity, so due panini is exactly what you expect.

Yes, but keeping it near tenuto is very natural because tenere da parte functions as a fixed expression.

The original:

• mi ha tenuto da parte due panini

A possible alternative:

• ha tenuto due panini da parte per me

That also works, but it is a bit heavier.

So the original word order is good because:

• mi comes before the auxiliary
• ha tenuto da parte stays together as the verbal idea
• due panini comes after

That makes the sentence flow naturally.

Perché is written with an accent when it means:

• because
• why in indirect constructions

In this sentence, it means because, so the accent is required:

• ..., perché sapeva che arrivavo tardi.

The accent is part of the normal spelling of the word.

They are related, but not always identical.

• mettere da parte often means to put aside
• tenere da parte often means to keep aside / keep reserved

In a shop context, tenere da parte is especially common for something saved for a customer.

So here tenere da parte is a very good choice because the baker did not just place the rolls somewhere; he kept them available for the speaker.

That is why the phrase feels so natural in this sentence.