La yema queda mejor si no cocinas el huevo demasiado.

Yes. Yema has several meanings in Spanish, including bud (on a plant) and fingertip, but in the context of el huevo it clearly means egg yolk.

So in this sentence:

• La yema = the yolk

Context usually makes the meaning obvious.

Spanish often uses the definite article more freely than English, especially when talking about things in a general or natural way.

So:

• La yema queda mejor literally = The yolk turns out better / is better
• si no cocinas el huevo demasiado literally = if you don’t cook the egg too much

In natural English, we often drop the in broader statements, but Spanish commonly keeps it.

Quedar here means something like:

• to turn out
• to end up
• to come out

So queda mejor means:

• turns out better
• comes out better
• is better that way

This is different from es mejor, which usually means is better in a more general or abstract sense.

Compare:

• La yema es mejor = The yolk is better
  (a more general statement, and a bit odd on its own)
• La yema queda mejor = The yolk comes out better / turns out better
  (talking about the result after cooking)

So queda is used because the sentence is about the result of cooking.

Queda is the present tense of quedar. Spanish often uses the present tense for:

• general truths
• instructions
• things that are usually the case

So the sentence means something like:

• The yolk comes out better if you don’t cook the egg too much

It is not talking about one specific future event, but about a general cooking principle.

After si meaning if, Spanish normally uses the present indicative for real or likely conditions.

So:

• si no cocinas el huevo demasiado = if you don’t cook the egg too much

That is why cocinas is correct.

Cocines is the present subjunctive, and it is generally not used after si in this kind of condition.

Compare:

• Si no cocinas el huevo demasiado, la yema queda mejor.
  = a normal real condition
• Quiero que no cocines el huevo demasiado.
  = subjunctive after quiero que

Cocinas is the tú form of cocinar, so yes, it literally means you cook.

Spanish often leaves out the subject pronoun because the verb ending already shows who the subject is.

So:

• (tú) cocinas = you cook

In this sentence, you is being used in the general sense, like English does in cooking advice:

• The yolk comes out better if you don’t cook the egg too much.

It doesn’t necessarily mean one specific person.

In Spanish, no normally goes directly before the conjugated verb.

So:

• no cocinas = you do not cook

That is the standard word order.

Compare:

• No como carne. = I don’t eat meat.
• No quiero eso. = I don’t want that.

So si no cocinas el huevo demasiado literally follows the usual pattern: if not you-cook the egg too much.

Here demasiado means:

• too much
• overly
• excessively

It modifies the action cocinas:

• cocinas el huevo demasiado = you cook the egg too much

Putting demasiado after the object is very natural in Spanish. You could think of it as modifying the whole action.

This is similar to:

• Hablas demasiado. = You talk too much.
• Lo calientas demasiado. = You heat it too much.

You could, but it would not mean quite the same thing.

• La yema queda mejor = The yolk turns out better / comes out better
• La yema está mejor = The yolk is better / the yolk is in a better state

Queda mejor focuses on the result of the cooking process, which is why it fits especially well here.

Yes, cocer can definitely be used for eggs, especially when you mean to boil them.

• cocinar = to cook in a general sense
• cocer = to boil / cook in water

So if the context is specifically boiling eggs, you might also hear:

• La yema queda mejor si no cueces demasiado el huevo.

That would mean more specifically:

• The yolk comes out better if you don’t boil the egg too much.

The original sentence with cocinas is broader and more general.

Yes, absolutely. That version is completely natural.

Both are correct:

• La yema queda mejor si no cocinas el huevo demasiado.
• Si no cocinas el huevo demasiado, la yema queda mejor.

The meaning stays the same. The difference is mostly one of emphasis:

• starting with La yema queda mejor... emphasizes the result
• starting with Si no cocinas... emphasizes the condition

It is mainly giving general advice by stating a general fact.

It also contains a comparison because of mejor:

• mejor = better

But the overall effect is something like practical cooking advice:

• The yolk comes out better if you don’t overcook the egg.

So it combines:

• a general truth
• a comparison
• an advisory tone