Mi abuela dice que hay que escurrir bien la pasta antes de mezclarla con la salsa.

Hay que is an impersonal expression meaning one has to, you have to, or it’s necessary to in a general sense.

So:

• Hay que escurrir bien la pasta = You have to drain the pasta well / The pasta needs to be drained well

It does not say who specifically has to do it. It sounds like general cooking advice.

Compare:

• Hay que escurrir bien la pasta = people in general should do this
• Tienes que escurrir bien la pasta = you have to do this
• Tenemos que escurrir bien la pasta = we have to do this

In recipes, instructions, and general advice, hay que is very common.

Escurrir means to drain, to strain off the liquid, or to let something drip dry.

In this sentence, it means draining the water from the pasta after cooking it.

Examples:

• Escurrir la pasta = to drain the pasta
• Escurrir las verduras = to drain the vegetables
• Escurrir el arroz = to drain the rice

In kitchen Spanish, escurrir is a very natural verb.

Here bien means well/properly, and it modifies the verb escurrir.

So:

• escurrir bien la pasta = to drain the pasta well

This word order is very normal in Spanish: verb + adverb + object.

Compare:

• Cocina bien la carne = Cook the meat well
• Lava bien las verduras = Wash the vegetables well
• Escurre bien la pasta = Drain the pasta well

You could sometimes move bien for emphasis, but escurrir bien la pasta is the most natural order here.

Spanish often uses the definite article more than English does, especially with food and general nouns.

So Spanish says:

• la pasta
• la salsa

where English might simply say:

• pasta
• sauce

In this sentence, la pasta refers to the pasta being prepared, so the article sounds completely natural.

Compare:

• Pongo la pasta en la olla. = I put the pasta in the pot.
• Me gusta la pasta. = I like pasta.

In English, we often drop the article, but in Spanish it is frequently required.

In Spanish, pasta is usually treated as an uncountable singular noun, like in English when we say Pasta is ready.

So:

• la pasta = pasta
• la pasta está lista = the pasta is ready

Even though pasta consists of many pieces, the noun itself is grammatically singular.

If you want to talk about specific types or pieces, Spanish would use other words, but in normal cooking language la pasta is singular.

After antes de (before), Spanish normally uses an infinitive when the subject stays general or is the same.

So:

• antes de mezclarla con la salsa = before mixing it with the sauce

This structure is very common:

• antes de comer = before eating
• antes de salir = before leaving
• antes de servirla = before serving it

So the pattern is:

• antes de + infinitive

That is exactly what is happening here.

Because la is a direct object pronoun, and with an infinitive it is very common to attach the pronoun to the end.

So:

• mezclar + la → mezclarla

This means to mix it.

With infinitives, Spanish allows object pronouns to be attached directly:

• comerlo = to eat it
• hacerla = to do/make it
• servirlos = to serve them

In this sentence:

• mezclarla con la salsa = to mix it with the sauce

That attached pronoun is completely standard.

La refers back to la pasta.

So the sentence is saying:

• drain the pasta well before mixing it with the sauce

Because pasta is feminine singular, the pronoun must also be feminine singular:

• la pasta → la

If the noun were masculine, you would use lo:

• el arroz → mezclarlo
• el pollo → cortarlo

Yes, you could, but it would be less explicit.

• antes de mezclarla con la salsa = before mixing it with the sauce
• antes de mezclar con la salsa = before mixing with the sauce

The version with la is clearer because it states exactly what is being mixed: the pasta.

In natural Spanish, repeating the object with a pronoun like this is very common and sounds good.

Because decir que means to say that.

So:

• Mi abuela dice que... = My grandmother says that...

This is one of the most common sentence patterns in Spanish:

• Creo que... = I think that...
• Sé que... = I know that...
• Dice que... = He/She says that...

In English, we often drop that:

• My grandmother says you have to...

But in Spanish, que is usually kept.

Usually it suggests a general statement, habitual opinion, or something she says as advice.

• Mi abuela dice que... = My grandmother says that...

The present tense dice can mean:

• she says (in general)
• she says / is saying (in this context)

Here it sounds like a general piece of advice or a typical family cooking rule.

If you wanted to make it clearly past, you would say:

• Mi abuela dijo que... = My grandmother said that...

Because the verb mezclar commonly uses con to mean to mix something with something else.

So:

• mezclar la pasta con la salsa = to mix the pasta with the sauce

That is the normal preposition here.

Examples:

• Mezcla el arroz con las verduras. = Mix the rice with the vegetables.
• Mezcla la harina con el agua. = Mix the flour with the water.

Using a here would not be the normal choice.

A recipe would usually drop Mi abuela dice que... and use either an imperative or an impersonal instruction.

For example:

• Escurre bien la pasta antes de mezclarla con la salsa.
  = Drain the pasta well before mixing it with the sauce.

Or:

• Hay que escurrir bien la pasta antes de mezclarla con la salsa.
  = You have to drain the pasta well before mixing it with the sauce.

The original sentence sounds more conversational because it introduces the advice with My grandmother says...

In standard Spanish from Spain, hay is pronounced roughly like eye in English.

A simple guide:

• hay ≈ eye
• que ≈ keh
• escurrir ≈ eh-skoo-REER
• mezclarla ≈ meth-KLAR-la in much of Spain, where z is pronounced like th in think

A full rough pronunciation:

• Mi abuela dice que hay que escurrir bien la pasta antes de mezclarla con la salsa
• mee ah-BWEH-lah DEE-theh keh eye keh eh-skoo-REER byEN lah PAS-tah AN-tes deh meth-KLAR-lah kon lah SAL-sah

In parts of Spain, z and soft c are pronounced with the th sound; in Latin America they are usually pronounced like s.