Ao provar a primeira fatia, notei logo o sabor da canela.

Ao + infinitive is a very common structure in Portuguese. Here, ao provar means when tasting, upon tasting, or as soon as I tasted.

So:

• ao provar = when/upon tasting
• ao chegar = when arriving
• ao abrir = when opening

In this sentence, Ao provar a primeira fatia sets the scene: When I tasted the first slice...

It is slightly more compact and elegant than using a full clause like Quando provei a primeira fatia.

Yes. Quando provei a primeira fatia, notei logo o sabor da canela is perfectly natural and means almost the same thing.

The difference is mostly stylistic:

• Ao provar... sounds a bit more literary or descriptive.
• Quando provei... is more straightforward and explicit.

Both are correct in European Portuguese.

Yes. Provar has more than one meaning, so context matters.

Common meanings include:

• to taste food: provar um bolo
• to try on clothes: provar uma camisa
• to prove something: provar uma teoria

In this sentence, because we are talking about a primeira fatia and o sabor da canela, provar clearly means to taste.

Yes. Fatia usually means slice, especially a slice of cake, pie, bread, ham, cheese, and similar things.

Examples:

• uma fatia de bolo = a slice of cake
• uma fatia de pão = a slice of bread

So a primeira fatia means the first slice.

Notei is the pretérito perfeito of notar, and it expresses a completed action in the past:

• notei = I noticed

It fits well because the sentence refers to a specific moment: after tasting the first slice, the speaker noticed the cinnamon flavour.

Compare:

• notei = I noticed / I did notice
• notava = I used to notice / I was noticing
• tenho notado = I have been noticing

Here, notei is the natural choice because it refers to one clear event.

No. In Portuguese, logo often means immediately, right away, or clearly from the start.

So:

• notei logo = I noticed straight away / I immediately noticed

This is a very common word in Portuguese, and its meaning is completely different from the English noun logo.

In European Portuguese, logo is extremely frequent in everyday speech.

Both are possible, but they are slightly different in structure.

• o sabor da canela = the flavour of the cinnamon
• sabor de canela = cinnamon flavour / flavour of cinnamon

In your sentence, notei logo o sabor da canela sounds very natural and specific: the speaker noticed the taste/flavour of the cinnamon in the slice.

Portuguese often uses the definite article more than English does, so o sabor da canela is very normal.

Portuguese often omits subject pronouns when the verb ending already makes the subject clear.

• notei clearly means I noticed
• so eu is optional

You could say:

• Ao provar a primeira fatia, notei logo o sabor da canela.
• Ao provar a primeira fatia, eu notei logo o sabor da canela.

Both are correct. The version without eu is more neutral and very common.

Yes, it is appropriate here.

The first part, Ao provar a primeira fatia, is an introductory clause. The comma separates that introductory element from the main clause:

• Ao provar a primeira fatia,
• notei logo o sabor da canela.

This is standard punctuation and helps readability.

A close natural translation could be:

• When I tasted the first slice, I immediately noticed the cinnamon flavour.
• Upon tasting the first slice, I immediately noticed the taste of cinnamon.
• As soon as I tasted the first slice, I noticed the cinnamon right away.

The exact English version depends on how literal or natural you want to be, but the Portuguese sentence clearly suggests an immediate perception.

Usually, yes: canela means cinnamon in food contexts.

Examples:

• bolo de canela = cinnamon cake
• chá com canela = tea with cinnamon

One thing to be aware of is that canela can also mean shin in body-related contexts. For example:

• bati com a canela na mesa = I hit my shin on the table

In your sentence, because of sabor, it clearly means cinnamon.

Yes, although the nuance and rhythm may change slightly.

Possible positions:

• notei logo o sabor da canela
• logo notei o sabor da canela
• notei o sabor da canela logo

The first one is very natural.
The second gives a bit more emphasis to logo.
The third is possible in some contexts, but less neutral here.

For this sentence, notei logo o sabor da canela is a very good, idiomatic choice.