Η σφολιάτα ήταν τόσο ζεστή, που η γέμιση έμενε μέσα ζεστή για πολλή ώρα.

Because it describes two different things:

• η σφολιάτα ήταν τόσο ζεστή = the pastry was so hot/warm
• η γέμιση έμενε μέσα ζεστή = the filling stayed warm inside

In Greek, the adjective has to agree with the noun it describes, and here both σφολιάτα and γέμιση are feminine singular, so the form is ζεστή both times.

τόσο ... που is a very common Greek structure meaning so ... that.

So:

• τόσο ζεστή, που... = so hot/warm that...

It works like English:

• Ήταν τόσο κουρασμένος, που κοιμήθηκε αμέσως.
• He was so tired that he fell asleep immediately.

In your sentence, the first part gives the degree, and the που clause gives the result.

They are both past forms, but they do slightly different jobs.

• ήταν = was
• έμενε = was staying / remained / stayed

Here:

• η σφολιάτα ήταν τόσο ζεστή describes a state in the past
• η γέμιση έμενε μέσα ζεστή για πολλή ώρα emphasizes that the filling continued to stay warm for some time

So έμενε is a good choice because it suggests duration or continuation, not just a simple fact.

Because the sentence is talking about something that lasted for a period of time in the past.

The imperfect in Greek often shows:

• ongoing action
• repeated action
• a continuing state

Here, έμενε ζεστή για πολλή ώρα means the filling remained warm for a long time, so the imperfect fits naturally.

If you used an aorist form instead, it would sound more like a completed event, not an ongoing state.

Here μέσα means inside.

In this sentence, it refers to the filling being warm inside the pastry.

So:

• η γέμιση έμενε μέσα ζεστή = the filling stayed warm inside

Greek often uses μέσα in a very natural, compact way like this, where English might say inside or on the inside.

Because ώρα is a feminine noun, and the word meaning much/a lot of has to agree with it.

So:

• masculine: πολλός
• feminine: πολλή
• neuter: πολύ

Since ώρα is feminine, the correct form is:

• πολλή ώρα = a long time

Compare:

• πολλός κόσμος = many people
• πολλή ζέστη = a lot of heat
• πολύ νερό = a lot of water

Because both nouns are feminine singular, and η is the feminine singular definite article, meaning the.

So:

• η σφολιάτα = the puff pastry / the pastry
• η γέμιση = the filling

Greek articles are used very regularly, much more than in English, and they must agree with the noun in gender, number, and case.

σφολιάτα literally refers to puff pastry or a pastry made with flaky layered dough.

Depending on context, it can mean:

• the dough itself
• a pastry item made from that dough

In this sentence, it most likely refers to the pastry as a whole, with filling inside.

It can be either, depending on context.

ζεστός / ζεστή / ζεστό covers both warm and hot in many situations. In this sentence:

• the pastry was so hot/warm
• the filling stayed warm

English often distinguishes more sharply between hot and warm, but Greek ζεστός can cover a broader range.

If you wanted something more like very hot / burning hot, Greek might use words such as καυτός in some contexts.

Greek word order is more flexible than English word order.

Here, ζεστή is still describing η γέμιση, even though μέσα comes before it. The sense is:

• the filling remained inside warm
• more naturally in English: the filling stayed warm inside

Greek often allows adverbs like μέσα to appear between the verb and the adjective without causing confusion.

You could also hear slightly different word orders in Greek, depending on style and emphasis.

Because που introduces a result clause after τόσο.

The pattern:

• τόσο ..., που ...

is normally written with a comma before που, just like English often separates so ... that ... clauses in writing.

So the comma helps show the structure:

• first: it was so warm/hot
• then: that the filling stayed warm inside for a long time

Yes. Greek allows several natural variations. For example, you might see:

• Η σφολιάτα ήταν τόσο ζεστή που η γέμιση έμενε ζεστή μέσα για πολλή ώρα.
• Η σφολιάτα ήταν τόσο ζεστή, ώστε η γέμιση να μένει μέσα ζεστή για πολλή ώρα.

The original sentence is perfectly natural, but Greek often gives you some freedom with:

• comma use
• word order
• whether you use που or a more formal option like ώστε

The adjective ζεστή agrees with each feminine singular noun it describes:

• η σφολιάτα → feminine singular → ζεστή
• η γέμιση → feminine singular → ζεστή

This is a basic Greek rule: adjectives must agree with the noun in:

• gender
• number
• case

So even though English just uses hot or warm without changing the form, Greek changes the adjective form to match the noun.