Si tu veux, nous pourrons en préparer une autre dimanche, et cette fois je te laisserai garnir la tarte toi-même.

In French, after si meaning if, you normally do not use the future tense for a real condition.

So French says:

• Si tu veux, nous pourrons...
• literally: If you want, we will be able to...

This is a very common pattern:

• Si tu viens, je serai content.
• If you come, I’ll be happy.

Even though English often uses a present tense after if too, English speakers sometimes expect the future because the second clause is in the future. French still keeps veux in the present.

A useful pattern to remember:

• si + present, future
• Si tu veux, je le ferai.

Nous pourrons is the future tense of pouvoir, meaning to be able to or can.

• nous pouvons = we can / we are able to
• nous pourrons = we will be able to / we can later

Here it suggests possibility in the future:

• nous pourrons en préparer une autre dimanche
• we’ll be able to make another one on Sunday

French often uses pouvoir where English might simply use can or sometimes not translate it very strongly at all.

En is a pronoun that usually replaces de + noun or refers back to an indefinite quantity or item already mentioned.

Here, en means something like of it / one of those / some more depending on context.

So:

• préparer une autre = prepare another one
• en préparer une autre = prepare another one of that kind / of those

If the earlier context was about pies or tarts, then en refers back to that category.

This is very common in French:

• Tu veux des pommes ? J’en prends deux. = Do you want apples? I’m taking two of them.
• Il fait des gâteaux ? Il en fait souvent. = Does he make cakes? He makes them often.

English often does not need an equivalent word, but French does.

Because autre agrees with the noun it replaces or describes.

Here, une autre is feminine singular, so the implied noun is feminine, most likely tarte.

• une autre tarte = another tart/pie
• en préparer une autre = make another one

Compare:

• un autre gâteau = another cake
• une autre tarte = another tart

Even when the noun is not repeated, the article still shows gender and number.

In this sentence, dimanche means on Sunday, so French can use the day name without an article.

• dimanche = on Sunday
• lundi = on Monday

Examples:

• On se voit mardi. = We’ll see each other on Tuesday.
• Je pars samedi. = I’m leaving on Saturday.

If you say le dimanche, it usually means on Sundays or on Sunday in general:

• Je fais du sport le dimanche. = I do sports on Sundays.

So here:

• dimanche = this coming Sunday / Sunday, in the context of the plan being discussed

Cette fois means this time.

It contrasts the coming attempt with a previous one. It suggests something like:

• last time, maybe I did the filling myself
• this time, I’ll let you do it

It is a very common expression:

• Cette fois, je comprends. = This time, I understand.
• Essaie encore, mais cette fois plus lentement. = Try again, but this time more slowly.

After laisser, French uses a direct object + infinitive structure:

• laisser quelqu’un faire quelque chose
• to let someone do something

So:

• je te laisserai garnir la tarte
• I’ll let you fill/top the tart

No de is used here.

Other examples:

• Je le laisse parler. = I let him speak.
• Elle nous laissera entrer. = She will let us come in.

This is similar to other causative/permissive structures in French.

Te means you and refers to the person being allowed to do the action.

So the structure is:

• je = I
• te = you
• laisserai = will let
• garnir la tarte = fill/top the tart

Literally:

• I will let you fill the tart

This te is the object of laisser.

Compare:

• Je te laisse choisir. = I let you choose.
• Je vais te montrer. = I’m going to show you.

Because after laisser, the second verb stays in the infinitive.

French uses:

• laisser + someone + infinitive

So:

• je te laisserai garnir
• not je te laisserai garnis
• not je te laisserai garniras

This is the same pattern as:

• Je vais te faire manger. = I’m going to make you eat.
• Je l’entends chanter. = I hear him sing.

The conjugated verb is laisserai; garnir remains unconjugated.

Because French uses the stressed pronoun toi, not the subject pronoun tu, in this kind of emphatic expression.

So:

• toi-même = yourself
• moi-même = myself
• lui-même = himself
• elle-même = herself
• nous-mêmes = ourselves

In the sentence, toi-même adds emphasis:

• je te laisserai garnir la tarte toi-même
• I’ll let you fill the tart yourself

It highlights that you will personally do it.

They both refer to you, but they do different jobs.

• te is the normal object pronoun required by the verb laisser
• toi-même is an emphatic phrase meaning yourself

So the sentence has both because each has a separate function:

• je te laisserai = I will let you
• toi-même = yourself, personally

Compare in English:

• I’ll let you do it yourself.

You still need both you and yourself.

Often yes, but it depends on context.

Garnir can mean:

• to fill
• to top
• to garnish
• to add the filling/topping to

With a tart, it can refer to putting the fruit or filling into/on the tart base.

So garnir la tarte might be translated naturally as:

• fill the tart
• top the tart
• add the filling to the tart

The exact English choice depends on what kind of tart it is.

The structure is:

• Si tu veux = If you want
• nous pourrons = we will be able to / we can
• en = of it / another one of those
• préparer = prepare
• une autre = another one
• dimanche = on Sunday

A key thing to notice is the position of en: it comes before the infinitive it belongs to.

This is normal in French:

• Je vais en acheter. = I’m going to buy some.
• Nous pourrons en préparer une autre. = We’ll be able to make another one.

Yes. In everyday spoken French, on is very often used instead of nous.

So these are both natural:

• nous pourrons en préparer une autre dimanche
• on pourra en préparer une autre dimanche

The difference is mostly one of style/register:

• nous pourrons sounds a bit more careful or formal
• on pourra sounds more conversational

Both are correct.

French, like English, can leave the noun unstated when it is already clear from context.

So instead of repeating tarte, French can simply say:

• une autre

This works just like English another one.

Compare:

• Je prends une tarte, et toi ? — Moi aussi, j’en prends une.
• Tu en veux une autre ?

The sentence avoids repetition because the listener already knows what kind of thing is being discussed.

Because the speaker is talking about a future plan or promise.

• nous pourrons = we will be able to
• je te laisserai = I will let you

This gives the sentence a clear future meaning: if the condition is met, these things will happen later.

French future endings are worth noticing here:

• pourrons = future of pouvoir with nous
• laisserai = future of laisser with je

Even though English sometimes uses we can for future plans, French often prefers an actual future tense in this kind of sentence.