Avant d’utiliser le moule, nous mettons un peu de beurre dedans pour que la tarte ne colle pas.

Because de becomes d’ before a vowel sound to avoid a clash of sounds. This is called elision.

• de utiliser → d’utiliser
• Similar examples:
  • d’accord
  • d habitude
  • d aimer → d’aimer

So avant d’utiliser is just the normal shortened form.

French uses avant de + infinitive when the subject of both actions is the same.

In this sentence:

• nous mettons = we put
• utiliser refers to what we do as well

So French says:

• Avant d’utiliser le moule, nous mettons...

This is like saying Before using the mold/pan, we put...

If the subject changed, French would usually use avant que + subjunctive instead.

Example:

• Avant que la tarte ne cuise...
• Before the tart bakes...

Le moule means the mold, the tin, or the baking pan, depending on context.

In cooking French, un moule is a container that gives shape to something while it cooks, such as:

• a cake pan
• a tart tin
• a mold

The exact English word depends on what kind of dish is being made. Since the sentence mentions la tarte, tart tin or tart pan is a very natural translation.

Yes. Both are possible.

• nous mettons = we put
• on met = literally one puts, but very often it means we put in everyday spoken French

So:

• Nous mettons un peu de beurre... is a little more neutral or formal
• On met un peu de beurre... sounds more conversational

A French recipe or explanation can use either style.

After un peu de, French normally uses de by itself.

So you say:

• un peu de beurre
• un peu d’eau
• un peu de sucre

This is because un peu de means a little bit of, and the de introduces the substance or quantity.

You would not normally say un peu du beurre unless you specifically meant a little of the butter, referring to some already identified butter in a special context.

Because after an expression of quantity, French usually uses de without the usual partitive article.

Compare:

• Nous mettons du beurre = We put some butter
• Nous mettons un peu de beurre = We put a little butter

Once you add a quantity expression such as:

• un peu de
• beaucoup de
• assez de
• trop de

the noun normally follows plain de.

Dedans means in it or inside.

Here it refers back to le moule:

• nous mettons un peu de beurre dedans = we put a little butter in it

French could also say:

• nous mettons un peu de beurre dans le moule

That is also correct. Using dedans avoids repeating le moule.

In more compact French, you might also hear:

• nous y mettons un peu de beurre

where y also means in it / there.

Because pour que introduces a clause with its own verb.

Here we have:

• pour que la tarte ne colle pas

This contains a full clause:

• subject: la tarte
• verb: colle

French uses:

• pour + infinitive when the subject stays the same
• pour que + subjunctive when there is a new subject

Compare:

• Nous beurrons le moule pour éviter les problèmes.
• We butter the pan to avoid problems.

Same subject, so pour + infinitive.

But in your sentence:

• la tarte is the subject of colle
• so French needs pour que

Because pour que is followed by the subjunctive in standard French.

So:

• pour que la tarte ne colle pas

The verb coller here is in the present subjunctive:

• que je colle
• que tu colles
• qu’il / elle colle
• que nous collions
• que vous colliez
• qu’ils / elles collent

The idea is one of purpose: we do this so that the tart will not stick.

In this particular form, you often cannot tell just by looking at it, because many -er verbs have the same spelling in the present indicative and present subjunctive for some persons.

For il / elle:

• indicative: elle colle
• subjunctive: qu’elle colle

So the clue comes from the structure:

• pour que strongly signals the subjunctive

In other words, the grammar around the verb tells you the mood.

That is the normal French negation pattern:

• ne
  • verb + pas

So:

• elle colle = it sticks
• elle ne colle pas = it does not stick

In everyday spoken French, people often drop ne:

• la tarte colle pas

But in careful written French, ne ... pas is expected.

French often uses the definite article in a general or context-known way.

Here la tarte does not necessarily mean one specific tart already identified in a detailed way. It can simply mean:

• the tart you are making
• tart in this situation

French uses the definite article more often than English in these kinds of practical instructions.

So la tarte ne colle pas is very natural.

Yes, but the tone changes a little.

• pour que = the most common everyday choice
• afin que = more formal, more careful, sometimes more literary

So these are both grammatical:

• ... pour que la tarte ne colle pas
• ... afin que la tarte ne colle pas

In ordinary speech and simple instructions, pour que is much more likely.

They are close in meaning, but not used in exactly the same way.

• Avant d’utiliser le moule is the normal choice when the subject is the same and you want a smooth, compact structure.
• Avant que nous utilisions le moule is grammatically possible, but heavier and much less natural here.

French strongly prefers avant de + infinitive when the subject is the same.

So in this sentence, avant d’utiliser is the natural option.