De postre quiero flan casero.

In Spanish, de postre is a fixed expression meaning for dessert or as dessert.

So:

• De postre quiero flan casero. = For dessert, I want homemade flan.

Here, de does not translate literally as of. Spanish often uses de in idiomatic expressions where English uses a different preposition.

You may also hear:

• ¿Qué quieres de postre? = What do you want for dessert?
• Tomé fruta de postre. = I had fruit for dessert.

So it is best to learn de postre as a complete chunk.

Spanish word order is flexible. Putting de postre first highlights it as the topic:

• De postre quiero flan casero.

This is like saying:

• As for dessert, I want homemade flan.

You could also say:

• Quiero flan casero de postre.

That version is also natural and means the same thing. The original sentence puts a little more focus on dessert.

Quiero is the first person singular form of querer in the present tense.

• querer = to want
• quiero = I want

So:

• quiero flan casero = I want homemade flan

A few other forms:

• quieres = you want
• quiere = he/she/it wants
• queremos = we want

Also note that querer is an irregular verb:

• e changes to ie in many forms:
  quiero, quieres, quiere, quieren
• but not in queremos or queréis

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

• Quiero flan casero. = I want homemade flan.
• Quiero un flan casero. = I want a homemade flan.

Without un, Spanish often talks about the food more generally, which is very natural when ordering or choosing dishes.

Compare:

• Quiero café. = I want coffee.
• Quiero un café. = I want a coffee.

With desserts, both can work depending on context. If you are choosing from a menu, Quiero flan casero sounds very natural.

Here casero means homemade or home-style.

So:

• flan casero = homemade flan

In many food contexts, casero/casera suggests something made in a traditional, non-industrial way.

Examples:

• comida casera = home cooking / homemade food
• pan casero = homemade bread
• salsa casera = homemade sauce

Depending on context, it can sometimes mean made at home, home-style, or traditional.

In Spanish, adjectives usually come after the noun.

So:

• flan casero = homemade flan

This is the normal order:

• vino tinto = red wine
• pan integral = wholemeal bread
• sopa caliente = hot soup

Some adjectives can come before the noun, but with casero, the normal and natural position here is after the noun.

Because casero has to agree with flan, and flan is a masculine singular noun.

Agreement in Spanish means adjectives change form to match the noun:

• flan casero — masculine singular
• tarta casera — feminine singular
• postres caseros — masculine plural
• galletas caseras — feminine plural

So the ending changes depending on the noun it describes.

Yes. Postre is the standard word for dessert in Spanish.

Examples:

• ¿Qué hay de postre? = What’s for dessert?
• No tomo postre. = I don’t have dessert.

In English, depending on the variety, you might say dessert, pudding, or afters, but in Spanish postre is the general word.

Normally, no. In this context, Spanish uses de postre, not para postre.

• De postre quiero flan casero. = natural
• Para postre quiero flan casero. = not the usual expression

This is one of those cases where the preposition is just part of the standard phrase, so it is best to memorize de postre as a set expression.

Yes, it sounds natural in Spain.

It could be used:

• when ordering in a restaurant
• when saying what you want after the main course
• when choosing from several desserts

Very natural alternatives include:

• De postre, quiero flan casero.
• Quiero flan casero de postre.
• Yo quiero flan casero de postre. — with yo added for emphasis

All of these sound normal, but the original sentence is perfectly idiomatic.

In Spain Spanish, flan is pronounced roughly like flahn.

A few notes:

• The a is a clear short vowel, like the a in father
• The n is a normal n
• The word is one syllable: flan

Also, flan in Spanish refers to the familiar caramel custard dessert, and English actually borrowed the word from Spanish/French usage, so it is easy to recognize.