El pan salió tan crujiente que mi hermano pidió otra rebanada.

Here salió means something like came out or turned out, not left.

With food, salir is often used to talk about the result of cooking:

• El pan salió crujiente = the bread came out crispy
• La tortilla salió muy buena = the omelette turned out very good

So in this sentence, salió refers to how the bread ended up after being made or baked.

Salió is very natural when talking about the outcome of food or a process.

• salió crujiente = it came out crispy / turned out crispy
• quedó crujiente = it ended up crispy / it was left crispy

Both salió and quedó can work here, but salió is especially common for results in cooking.

Why not the others?

• fue crujiente is not natural here. It sounds wrong for describing the result of baking.
• estaba crujiente means it was crispy, which describes a state, but not so clearly the result of the cooking process.

So salió highlights the final outcome.

Tan... que means so... that.

Structure:

• tan
  • adjective/adverb + que
    • result

In your sentence:

• tan crujiente = so crispy
• que mi hermano pidió otra rebanada = that my brother asked for another slice

Similar examples:

• Estaba tan cansado que se durmió. = He was so tired that he fell asleep.
• Habla tan rápido que no entiendo nada. = He speaks so fast that I don’t understand anything.

So this sentence uses a very common Spanish pattern for cause/result.

Because crujiente is an adjective that has the same form for masculine and feminine singular.

Examples:

• el pan crujiente
• la galleta crujiente

And in the plural:

• los panes crujientes
• las galletas crujientes

So crujiente does agree in number, but not with a different masculine/feminine ending like -o / -a adjectives do.

Pidió is the preterite of pedir, and it is used because the sentence refers to a completed action in the past: your brother asked for another slice at a specific moment.

• pidió = he asked / he ordered
• pedía = he was asking / used to ask

Here, the idea is:

1. the bread came out very crispy
2. as a result, your brother asked for another slice

That is a clear completed event, so the preterite is the natural choice.

In Spanish, when otro / otra means another, you normally do not use un/una before it.

So:

• otra rebanada = another slice

Not:

• una otra rebanada ❌

This is different from English, where another historically includes the idea of an + other.

Compare:

• Quiero otra taza. = I want another cup.
• Pidió otra rebanada. = He asked for another slice.

But if you say la otra rebanada, that means the other slice, not another slice.

Rebanada means slice, especially a slice of bread or something cut into slices.

So otra rebanada is very natural for bread.

Other possible words are:

• trozo = piece
• porción = portion
• pedazo = piece/chunk

But they are not as specific as rebanada.

For bread:

• una rebanada de pan = a slice of bread

So in this sentence, rebanada is the best and most precise choice.

Because in modern Spanish, possessives like mi, tu, su, nuestro usually replace the article.

So you say:

• mi hermano = my brother
• tu casa = your house
• su coche = his/her car

Not:

• el mi hermano ❌

Older Spanish and some regional/literary styles may use forms like that, but in normal modern Spanish, mi hermano is the correct form.

The written accents show where the stress falls:

• salió = sa-LIÓ
• pidió = pi-DIÓ

These are third-person singular preterite forms:

• salir → salió
• pedir → pidió

The accent is important because it marks the correct pronunciation and distinguishes these forms from spellings that would follow different stress rules.

For learners, the key thing is: when you see -ió in forms like these, the stress falls on the final syllable.

Yes, it sounds natural in Spain.

Everything in the sentence is standard and widely understood:

• El pan salió... is natural for talking about how food turned out.
• crujiente is a very common word in Spain.
• rebanada is also standard and natural.

Depending on the speaker or region, someone might choose a slightly different noun such as trozo, but rebanada works very well here.

Yes, El pan quedó tan crujiente que... is also possible.

The difference is small:

• salió tan crujiente = the bread came out so crispy
• quedó tan crujiente = the bread ended up so crispy

Both are correct and natural.
In cooking contexts, both verbs can describe the final result, but salió often feels especially idiomatic when talking about how a dish turned out.

So the original sentence is perfectly good, but quedó would also be a reasonable alternative.