Eu quero usar as natas para fazer uma sobremesa simples.

You could absolutely drop Eu and say:

Quero usar as natas para fazer uma sobremesa simples.

In Portuguese, the subject pronoun is often omitted because the verb ending already shows who is doing the action.
Here, quero clearly means I want.

Including Eu is still correct. It can add:

• emphasis: Eu quero usar as natas...
• contrast: Eu quero usar as natas, mas ele não.

So in everyday Portuguese, leaving out Eu is very common.

Portuguese often uses the definite article with nouns where English may not.

So as natas means literally the cream, but in natural English we would usually just say cream.

This is very common with food and ingredients in Portuguese. For example:

• o pão = bread
• o leite = milk
• a manteiga = butter
• as natas = cream

You may also hear natas without the article in some contexts, but usar as natas sounds very natural.

This is just how Portuguese works with this word. In European Portuguese, natas is normally plural in form, even when it refers to cream as a single ingredient.

So:

• as natas = cream
• not a nata in this meaning

The singular nata does exist, but it usually refers to a layer of cream or scum on a liquid, not the ingredient in general.

So when cooking, as natas is the normal form.

Not exactly. This is an important European Portuguese vs Brazilian Portuguese difference.

In Portugal, natas is the usual word for cream.

In Brazil, people usually say creme de leite instead.

So this sentence sounds clearly European Portuguese:

• Eu quero usar as natas... → Portugal

A Brazilian equivalent would more likely be:

• Eu quero usar o creme de leite...

Para here expresses purpose: in order to or to.

So:

• usar as natas para fazer uma sobremesa
  = use the cream to make a dessert

This pattern is very common:

• Comprei ovos para fazer um bolo.
  = I bought eggs to make a cake.
• Preciso de açúcar para fazer doces.
  = I need sugar to make sweets.

After para, Portuguese often uses the infinitive when the subject stays general or is the same:

• para fazer = to make

Yes, but it changes the structure slightly.

• para fazer = to make
• para eu fazer = for me to make

In your sentence, para fazer is the most natural and simple choice because it already sounds clear.

Para eu fazer is more explicit and is used when you want to stress who will do the action, especially if it could be someone else:

• Guardei as natas para eu fazer a sobremesa amanhã.
  = I saved the cream so that I can make the dessert tomorrow.

So in your original sentence, para fazer is the best default option.

In Portuguese, adjectives usually come after the noun.

So:

• uma sobremesa simples = a simple dessert

This is the normal order:

• um carro novo = a new car
• uma ideia interessante = an interesting idea
• uma sobremesa simples = a simple dessert

Some adjectives can come before the noun, but that often changes the tone or meaning. With simples, the usual and most natural position here is after the noun.

Simples is one of those adjectives that has the same form in masculine and feminine singular.

So you get:

• um prato simples
• uma sobremesa simples

In the plural, it becomes:

• simples as well in spelling, but the article/noun show the plural:
• pratos simples
• sobremesas simples

So the adjective itself stays the same in many forms.

Yes, sobremesa means dessert.

Literally, it comes from the idea of something served after the meal. It is the standard word for dessert in Portuguese.

Examples:

• Quero uma sobremesa. = I want a dessert.
• A sobremesa é deliciosa. = The dessert is delicious.

You may also hear doce, which means sweet and can sometimes refer to a sweet dish or treat, but sobremesa is the clearest word for dessert in this sentence.

Fazer is the most general and natural verb here. It means to make.

In Portuguese, just like in English, you often make a dessert:

• fazer uma sobremesa
• fazer um bolo
• fazer o jantar

Cozinhar means to cook, but desserts are not always thought of primarily as something cooked, and fazer is broader and more idiomatic in this context.

So:

• fazer uma sobremesa = the most natural choice

Yes, you could say:

Eu quero utilizar as natas para fazer uma sobremesa simples.

It is grammatically correct, but usar is more everyday and natural in casual speech.

• usar = common, simple, conversational
• utilizar = a bit more formal or more technical

So for normal conversation, usar is usually better.

In European Portuguese, quero is approximately pronounced like:

KEH-roo or more narrowly KEH-ru

A few helpful points:

• que- here sounds like keh
• the r is usually a tapped or lightly rolled r
• the final o in European Portuguese is often reduced, so it may sound closer to u than a full English oh

So quero does not usually sound like a fully open keh-roh in Portugal.

Yes, it sounds perfectly natural.

A speaker might also shorten it a little by dropping Eu:

Quero usar as natas para fazer uma sobremesa simples.

Other natural variations include:

• Quero usar as natas para fazer uma sobremesa fácil.
• Vou usar as natas para fazer uma sobremesa simples.

But your original sentence is completely normal and idiomatic in European Portuguese.