Una vez cocido el pollo, se puede mezclar todo y remover la sopa suavemente.

Here una vez means once or when, not one time in the counting sense.

In recipe-style Spanish, una vez + past participle / completed action is a very common way to mean once something has been done:

• Una vez cocido el pollo... = Once the chicken is cooked...
• Una vez terminada la salsa... = Once the sauce is finished...

So although una vez can literally mean one time in other contexts, here it introduces a time condition.

Una vez cocido el pollo is a shortened, compact way of saying:

• Una vez que el pollo esté cocido...
• Cuando el pollo esté cocido...

This kind of shortened structure is very common in written instructions, recipes, and formal procedural language.

So:

• Una vez cocido el pollo... = more concise, recipe-like
• Cuando el pollo esté cocido... = fuller and more explicit

English does something similar:

• Once the chicken is cooked...
• When the chicken is cooked...

It is originally a past participle, but here it behaves very much like an adjective meaning cooked.

It agrees with el pollo, which is masculine singular, so we get:

• el pollo cocido

If the noun changed, the form would change too:

• la carne cocida
• los huevos cocidos
• las verduras cocidas

So yes, it comes from a verb form, but in this sentence it is functioning adjectivally.

Both can be possible, but they are not always exactly the same in feel.

• cocido = cooked
• cocinado = cooked / prepared

In recipes, cocido is very common to mean that the food is done or cooked through. It is the more natural choice in many instructional contexts.

So:

• Una vez cocido el pollo... sounds very natural.
• Una vez cocinado el pollo... is grammatical, but it may sound a little less idiomatic in this kind of recipe sentence.

Se puede is an impersonal structure. It means something like:

• one can
• you can
• it is possible to

This is extremely common in recipes and instructions because it sounds neutral and general.

Compare:

• Se puede mezclar todo... = Everything can be mixed... / You can mix everything...
• Puedes mezclar todo... = directly addressing you
• Mezcla todo... = direct command: Mix everything

In recipes from Spain, se puede often gives a more impersonal, instructional tone.

Because they come after puede.

After poder, Spanish normally uses an infinitive:

• se puede mezclar
• se puede remover

This is the same pattern as English can + verb:

• can mix
• can stir

So:

• se puede mezclar todo y remover la sopa
  literally works like
• one can mix everything and stir the soup

They are similar, but not identical.

• mezclar = to mix, to combine
• remover = to stir, to move around with a spoon or utensil

So in the sentence:

• mezclar todo = combine all the ingredients / mix everything together
• remover la sopa suavemente = stir the soup gently

A very important point for English speakers: remover does not mean to remove here. It is a false friend in this context.

In Spain, remover is a very normal verb for stirring food.

Not always, but in cooking that is a very common meaning.

More generally, remover can mean to move, to stir up, or to unsettle depending on context. But in a recipe, if you see something like:

• remover la sopa
• remover la salsa
• remover bien

it usually means stir.

This is why learners should be careful not to interpret it as English remove.

Here todo means everything.

It is being used as a pronoun, not as an adjective.

• mezclar todo = mix everything

If it were describing a noun, you would need more structure:

• mezclar todos los ingredientes = mix all the ingredients

So:

• todo = everything
• todos los ingredientes = all the ingredients

Both are possible, but todo is shorter and very natural if the ingredients are already understood from context.

Because remover often takes a direct object telling you what you are stirring.

• remover la sopa = stir the soup
• remover la salsa = stir the sauce

Sometimes recipes just say remover suavemente if it is already obvious what is being stirred. But including la sopa makes the sentence clearer.

Suavemente means gently, softly, or lightly, depending on context.

Here it means gently, describing how you should stir the soup:

• remover la sopa suavemente = stir the soup gently

Its position is natural. Spanish adverbs in -mente often come after the verb phrase:

• remover la sopa suavemente

You could also hear:

• remover suavemente la sopa

Both are grammatical. The version in your sentence sounds very natural.

Yes, absolutely. That is the fuller version.

• Una vez cocido el pollo...
• Una vez que el pollo esté cocido...

Both mean essentially the same thing here.

The second version is more explicit because it includes the verb esté. The first version is more compact and stylistically very typical of instructions and recipes.

Because after expressions like una vez que, when you are referring to a future or not-yet-completed action, Spanish often uses the subjunctive.

So in a recipe, before the chicken has finished cooking, Spanish naturally says:

• Una vez que el pollo esté cocido...

That is the standard way to refer to something that will be completed before the next step happens.

Using está would sound more like a general statement or a description of a current situation, not the normal step-by-step recipe phrasing.

It is the normal punctuation here.

The opening part:

• Una vez cocido el pollo

is an introductory time phrase. In Spanish, it is very common to separate that from the main clause with a comma:

• Una vez cocido el pollo, se puede...

So yes, the comma is appropriate and recommended.

Yes. Several features make it sound like standard recipe or instruction language:

• Una vez... for sequencing steps
• se puede... for impersonal instructions
• mezclar and remover as cooking verbs
• the compact participle structure cocido el pollo

So even if other versions are possible, this sentence sounds very natural for written instructions in Spanish from Spain.