Mi hermana prefiere el brócoli al horno, pero mi madre quiere sopa de col.

In modern standard Spanish, possessive words like mi, tu, su, nuestro normally go before the noun without an article:

• mi hermana
• mi madre

Unlike in English, you do not say the my sister or the my mother, and Spanish does not normally say la mi hermana either.

Also notice that mi means both my (singular masculine noun) and my (singular feminine noun), so it stays the same with both hermana and madre.

Prefiere is the third-person singular present tense form of preferir:

• yo prefiero = I prefer
• tú prefieres = you prefer
• él/ella/usted prefiere = he/she/you prefer

Here the subject is mi hermana, which is she, so Spanish uses prefiere.

Also, preferir is a stem-changing verb in the present tense:
e → ie in most forms:

• prefiero
• prefieres
• prefiere
• preferimos
• preferís
• prefieren

So prefiere is the correct form.

Because preferir is one of many Spanish verbs with a stem change in the present tense. The e in the stem changes to ie in most forms.

Pattern:

• preferir
• yo prefiero
• tú prefieres
• él/ella prefiere
• nosotros preferimos
• vosotros preferís
• ellos prefieren

This is something learners just have to get used to, because English does not usually change the vowel inside the verb in this way.

Yes, el usually means the, but Spanish often uses the definite article more than English does, especially with food and general things.

So Spanish can say:

• prefiere el brócoli al horno

where English would often simply say:

• prefers baked broccoli

Spanish is more comfortable using the article with foods, body parts, and general categories.

Also, brócoli is treated as a masculine noun in standard Spanish, so it takes el.

Al horno means baked, oven-baked, or more literally in the oven / to the oven style depending on context.

The form al is a contraction of:

• a + el = al

So:

• al horno = literally to the oven / idiomatically oven-baked

This is a very common food expression in Spanish:

• pollo al horno = roast/baked chicken
• patatas al horno = baked potatoes
• brócoli al horno = baked broccoli

So in this sentence, el brócoli al horno means the baked broccoli.

Pero means but.

It connects two contrasting ideas:

• Mi hermana prefiere el brócoli al horno
• pero mi madre quiere sopa de col

So the sentence is contrasting what the sister prefers with what the mother wants.

Spanish often drops subject pronouns like yo, tú, ella, because the verb ending already gives that information. But in this sentence, the subjects are not pronouns — they are full nouns:

• mi hermana
• mi madre

They are repeated because the speaker is talking about two different people. If you removed them, the sentence would become unclear.

For example:

• Mi hermana prefiere el brócoli al horno, pero mi madre quiere sopa de col.

This clearly tells us who likes what.

Quiere is the present tense of querer and means wants here:

• mi madre quiere sopa de col = my mother wants cabbage soup

It is different from:

• querría = would want
• le gusta = likes

So:

• quiere sopa de col = she wants cabbage soup
• le gusta la sopa de col = she likes cabbage soup

Also, querer is another stem-changing verb:

• quiero
• quieres
• quiere

Spanish often omits the article after verbs like querer, especially when talking about something in a general or indefinite way.

So all of these can be possible, but they do not mean exactly the same thing:

• quiere sopa de col = wants cabbage soup (some cabbage soup / cabbage soup in general)
• quiere una sopa de col = wants a cabbage soup / a bowl of cabbage soup
• quiere la sopa de col = wants the cabbage soup (a specific one)

In your sentence, quiere sopa de col sounds natural and general.

Here de means of, so sopa de col is literally soup of cabbage.

Spanish often uses de where English uses a noun as an adjective:

• sopa de tomate = tomato soup
• zumo de naranja = orange juice
• ensalada de pollo = chicken salad

So sopa de col is the normal Spanish structure for cabbage soup.

Col is a general Spanish word for cabbage. In Spain, col is a normal and common word.

Depending on region, you may also hear:

• repollo = cabbage, often especially the round cabbage head
• col = cabbage, and also part of names of related vegetables

In Spain, col in sopa de col sounds perfectly natural.

Brócoli has a written accent because of Spanish stress rules.

The stress falls on the first syllable:

• BRÓ-co-li

Without the accent mark, Spanish pronunciation rules would suggest a different stress pattern. The accent tells you clearly where to stress the word.

This is useful for learners because it helps with pronunciation.

A careful Spain Spanish pronunciation would be approximately:

Mi er-MA-na pre-fye-re el BRÓ-co-li al ÓR-no, PE-ro mi MA-dre KYE-re SO-pa de KOL.

A few useful points:

• h in horno is silent.
• qu in quiere sounds like k.
• ll does not appear here, so that is not an issue.
• In most of Spain, c before e/i and z sound like the th in thin, but here col has c before o, so it is a normal k sound.
• r in pero is a soft tapped r, not the strong rolled rr.

Yes, but the meaning changes slightly.

• Mi hermana prefiere el brócoli al horno = My sister prefers baked broccoli
• A mi hermana le gusta más el brócoli al horno = My sister likes baked broccoli more

Both are natural, but preferir is more direct when talking about preference. Gustar más often feels a little more like comparing tastes.

So the original sentence is a very normal and straightforward way to express preference.