Je vais préparer une soupe de chou-fleur et de poireaux, parce qu’il fait froid ce soir.

Je vais préparer is the futur proche (near future), literally I am going to prepare. It is very common in everyday French when talking about something you are about to do or have decided to do.

• Je vais préparer une soupe = I’m going to make a soup
• Je préparerai une soupe = I will make a soup

Both are correct, but je vais préparer often sounds more natural in casual speech.

Because aller + infinitive is a fixed structure in French used to form the near future.

So:

• je vais préparer
• tu vas manger
• nous allons partir

You do not say je vais à préparer.

Une soupe means a soup or a bowl/type of soup as a countable dish.

• Je prépare une soupe = I’m making a soup / a soup dish
• Je mange de la soupe = I’m eating some soup

So here, the speaker is talking about making one specific soup, which is why une is used.

After de, when naming ingredients or the type of a dish, French often leaves out the article.

So:

• une soupe de chou-fleur
• une tarte aux pommes
• une salade de tomates

Here, de means something like made with or of.

That is why you do not see:

• une soupe du chou-fleur
• une soupe des poireaux

Those would sound wrong here.

Chou-fleur is a compound noun meaning cauliflower. French often uses hyphens in compound words.

• un chou-fleur = a cauliflower
• des choux-fleurs = cauliflowers

In modern usage, you will sometimes see spelling reforms that affect some hyphenated words, but chou-fleur with a hyphen is the standard form learners should use.

This is a very natural way to name ingredients in French. Ingredient nouns after de do not always behave exactly the same way.

• chou-fleur can be understood as the ingredient cauliflower in a general sense
• poireaux is plural because the dish is made with leeks, usually several of them

In food names, French can use either singular or plural depending on the ingredient and usage. The important point is that this phrase sounds natural as the name of a soup.

Parce que means because and introduces the reason for something.

• Je vais préparer une soupe... parce qu’il fait froid. = I’m going to make soup because it’s cold.

Car also means for/because, but it is usually more formal or written.

• Il fait froid, car c’est l’hiver.

In everyday speech, parce que is much more common.

This is elision. When que is followed by a word beginning with a vowel or silent h, the e drops and becomes qu’.

So:

• que il → qu’il
• que elle → qu’elle
• que on → qu’on

That is why you get:

• parce qu’il fait froid

not

• parce que il fait froid

It does not refer to a specific person or thing. This is an impersonal il, similar to the it in English weather expressions.

• Il pleut = It’s raining
• Il neige = It’s snowing
• Il fait froid = It’s cold

So il here is just the grammatical subject required by the verb.

French uses faire in many weather and temperature expressions.

• il fait froid = it’s cold
• il fait chaud = it’s hot
• il fait beau = the weather is nice
• il fait mauvais = the weather is bad

C’est froid usually means that is cold or it is cold in the sense that an object feels cold, not the general weather.

So in this sentence, il fait froid is the correct expression for the weather or the temperature outside.

Use:

• ce before most masculine singular nouns
• cet before a masculine singular noun that begins with a vowel or silent h

So:

• ce soir = this evening
• ce livre = this book
• cet hiver = this winter
• cet homme = this man

Because soir begins with s, the correct form is ce.

Ce soir can often move around, but at the end is very natural here:

• Il fait froid ce soir. = It’s cold tonight.

You could also say:

• Ce soir, il fait froid.

That puts more emphasis on tonight.

No, it is not strictly required. French punctuation is a little flexible here.

Both are possible:

• Je vais préparer une soupe de chou-fleur et de poireaux parce qu’il fait froid ce soir.
• Je vais préparer une soupe de chou-fleur et de poireaux, parce qu’il fait froid ce soir.

The comma can make the pause clearer, but many writers would leave it out.