La pasta con albahaca fresca siempre huele mejor cuando la hacemos en casa.

Because pasta is a feminine noun in Spanish, so it takes the feminine article la.

Spanish nouns have grammatical gender, and articles and adjectives must agree with them:

• la pasta
• la albahaca fresca

This gender is grammatical, not biological. You usually just have to learn the noun together with its article.

In Spanish, adjectives usually come after the noun, so albahaca fresca is the normal order for fresh basil.

Also, fresca is feminine singular because it agrees with albahaca, which is feminine singular:

• albahaca fresca
• tomate fresco
• verduras frescas

Putting the adjective before the noun is possible in some cases, but it often sounds more literary, emphatic, or changes the nuance.

Huele comes from the verb oler, which means to smell.

Here, la pasta con albahaca fresca is the subject, so huele means smells:

• La pasta huele bien = The pasta smells good
• La sopa huele raro = The soup smells strange

A useful detail: oler is a stem-changing verb in most present-tense forms:

• yo huelo
• tú hueles
• él/ella huele
• nosotros olemos
• vosotros oléis
• ellos huelen

So huele is the correct él/ella/usted form, used here because the subject is a singular thing: la pasta.

Mejor means better, and after a verb like oler it works naturally in Spanish:

• huele mejor = smells better

Spanish does not say huele más bueno here. That would sound unnatural.

Think of it like this:

• bueno / buena = good
• bien = well
• mejor = better

With verbs like oler, saber, verse, sentirse, Spanish often uses mejor:

• Esto sabe mejor = This tastes better
• Así se ve mejor = It looks better this way

That is a very common position for adverbs in Spanish. Siempre often goes before the conjugated verb:

• siempre huele mejor
• siempre sabe mejor
• siempre queda bien

It gives a natural rhythm and sounds very standard. Spanish word order is somewhat flexible, but this placement is one of the most common and natural ones.

Because here cuando is a conjunction meaning when, introducing a time clause:

• cuando la hacemos en casa = when we make it at home

Spanish uses cuándo with an accent in questions, direct or indirect:

• ¿Cuándo la hacemos? = When are we making it?
• No sé cuándo la hacemos. = I don’t know when we’re making it.

So:

• cuando = when
• cuándo = when? / at what time?

The la is a direct object pronoun, and it refers back to la pasta.

So:

• cuando la hacemos en casa literally means:
• when we make it at home

Spanish often uses an object pronoun instead of repeating the noun:

• cuando hacemos la pasta en casa
• cuando la hacemos en casa

Both are possible, but the second is smoother because it avoids repetition.

Hacemos is the we form of hacer in the present tense:

• yo hago
• tú haces
• él/ella hace
• nosotros hacemos

Spanish usually leaves out subject pronouns when the verb ending already makes the subject clear. So hacemos already means we make.

That is why:

• cuando la hacemos en casa is completely natural, and
• cuando nosotros la hacemos en casa would only be used if you wanted extra emphasis or contrast.

Because the sentence is talking about a general, habitual idea, not one specific occasion.

Spanish uses the present tense for things that are generally true or usually happen, just like English:

• Siempre huele mejor = It always smells better
• cuando la hacemos en casa = when we make it at home

So the sentence means something like a repeated experience: this is what normally happens.

En casa is the normal Spanish expression for at home.

So:

• en casa = at home
• en la casa = in the house

The version with the article usually refers more literally to the physical building, while en casa is the idiomatic expression for being at home or doing something at home.

Examples:

• Comemos en casa = We eat at home
• Estoy en casa = I’m at home
• Hay mucho ruido en la casa = There is a lot of noise in the house