Je sers la soupe avec une louche, mais Paul préfère utiliser une petite tasse.

Because servir is an irregular verb.

In the present tense, it goes:

• je sers
• tu sers
• il / elle / on sert
• nous servons
• vous servez
• ils / elles servent

So je sers la soupe means I serve the soup.

A useful thing to notice: the singular forms and the ils/elles form use ser-, while nous and vous keep serv-.

Here, servir means to serve, especially to serve food.

So Je sers la soupe means I am serving the soup or I serve the soup.

Be careful, because servir can have more than one meaning in French depending on the structure:

• servir quelque chose = to serve something
  
  • Je sers la soupe.
• se servir de quelque chose = to use something
  
  • Je me sers d’une louche.

That is one reason the sentence later uses utiliser: it avoids confusion and is very clear for learners.

Both are possible in French, but they do not mean exactly the same thing.

• Je sers la soupe = I am serving the soup
  This sounds like a specific soup already understood in the situation, such as the soup for the meal.
• Je sers de la soupe = I am serving some soup / soup in general

So la soupe is natural if the soup is a known dish in the context.

This is a common difference for English speakers, because English often says just soup, while French usually needs an article such as la, de la, une, etc.

Because avec can introduce the tool or instrument used to do something.

So:

• avec une louche = with a ladle
• more naturally in English: using a ladle

In this sentence, avec une louche tells you how the soup is being served.

Other similar examples:

• J’écris avec un stylo. = I write with a pen.
• Il coupe le pain avec un couteau. = He cuts the bread with a knife.

Because after préférer, French often uses an infinitive when you mean prefer to do something.

So:

• Paul préfère utiliser une petite tasse. = Paul prefers to use a small cup.

This is parallel to English:

• I prefer to wait.
• Je préfère attendre.

If you said Paul préfère une petite tasse, that would mean Paul prefers a small cup, but it would not explicitly say what he prefers to do with it.

There are two grammar points here:

1. Noun gender
Tasse is a feminine noun, so you need:

• une not un
• petite not petit

So the correct form is une petite tasse.

2. Adjective position
Many common short adjectives, including petit, usually come before the noun in French.

So:

• une petite tasse = a small cup

Not une tasse petite, which sounds unnatural here.

Yes, absolutely.

That would also be natural French:

• Paul préfère se servir d’une petite tasse.

Here, se servir de means to use.

So the two versions are close in meaning:

• préfère utiliser une petite tasse
• préfère se servir d’une petite tasse

The version with utiliser is very straightforward and easy to understand.
The version with se servir de is also common, but learners sometimes mix it up with servir meaning to serve.

The comma helps separate two full clauses:

• Je sers la soupe avec une louche
• Paul préfère utiliser une petite tasse

In French, it is very common to put a comma before mais when it links two clauses, especially when the subject changes, as it does here from je to Paul.

It is mainly a punctuation and readability choice. In a short sentence, you may sometimes see variation, but this comma is completely natural.

Yes. Une louche is the standard French word for a ladle.

It is feminine, so you say:

• une louche
• la louche

It is the usual kitchen utensil for serving soup or other liquids.

A careful pronunciation is:

Je sers la soupe avec une louche, mais Paul préfère utiliser une petite tasse.

Approximate IPA:

/ʒə sɛʁ la sup avɛk yn luʃ, mɛ pɔl pʁefɛʁ yt̬ilize yn pətit tas/

A rough English-friendly guide:

zhuh sair lah soop ah-vek eun loosh, meh Pol pray-fair ew-tee-lee-zay eun puh-teet tahss

A few useful pronunciation notes:

• Je is often a light zhuh
• sers sounds roughly like sair
• soupe rhymes roughly with English soup
• louche sounds like loosh
• mais sounds like meh
• préfère has an open è sound: pray-fair
• petite is puh-teet
• tasse sounds like tahss

Also, in normal speech, je may be pronounced very lightly.