Das Brot ist so knusprig, dass sogar mein Bruder noch ein Stück nimmt.

So ... dass is a very common pattern meaning so ... that.

• so knusprig = so crispy
• dass ... = that ...

So the structure is:

• Das Brot ist so knusprig, dass ...
• The bread is so crispy that ...

German uses this pattern just like English does.

Because dass introduces a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

Main clause:

• Das Brot ist so knusprig

Subordinate clause:

• dass sogar mein Bruder noch ein Stück nimmt

So nimmt goes to the end because of dass.

This is one of the most important German word-order rules to learn.

They are different words:

• das = the or that as a pronoun/article
• dass = that as a conjunction introducing a clause

In this sentence:

• Das Brot = the bread
• dass sogar mein Bruder ... nimmt = that even my brother takes ...

A useful shortcut:

• If it introduces a whole clause with a verb at the end, it is usually dass.

Sogar means even.

It adds the idea that this is somewhat surprising:

• dass sogar mein Bruder noch ein Stück nimmt
• that even my brother takes another piece

So the speaker is suggesting that the brother is maybe not usually interested, not easily impressed, or not expected to take more.

A close alternative is selbst in some contexts:

• dass selbst mein Bruder noch ein Stück nimmt

Both can mean even, though sogar often sounds a little more explicitly emphatic.

Here noch means something like another / one more / still depending on context.

In:

• noch ein Stück nimmt

the most natural sense is takes another piece.

So noch is not just still here. It suggests an extra amount:

• ein Stück = a piece
• noch ein Stück = another piece / one more piece

This is a very common use of noch.

Because German often uses Stück to mean piece when talking about food or portions.

• ein Stück Brot = a piece of bread
• noch ein Stück = another piece

In this sentence, Brot is understood already, so ein Stück is enough.

You could think of it as:

• another piece [of it]

Using eins would not sound as natural here, because the speaker is talking about a portion of bread, not just the number one by itself.

Mein Bruder is in the nominative case because it is the subject of nimmt.

Ask: who is taking another piece?

Answer: mein Bruder

So:

• mein Bruder = subject = nominative

The sentence inside the dass clause is basically:

• mein Bruder nimmt noch ein Stück

Ein Stück is in the accusative case because it is the direct object of nimmt.

Ask: what does my brother take?

Answer: ein Stück

So:

• subject = mein Bruder (nominative)
• object = ein Stück (accusative)

Here, ein Stück looks the same in nominative and accusative because Stück is neuter:

• nominative: ein Stück
• accusative: ein Stück

So the form does not change, but the function is accusative.

Because knusprig is being used as a predicate adjective, after the verb ist.

In German, adjectives used after verbs like sein, werden, and bleiben do not take adjective endings.

So:

• Das Brot ist knusprig.

But before a noun, the adjective would need an ending:

• das knusprige Brot

Compare:

• Das Brot ist knusprig.
• Ich esse das knusprige Brot.

Because in German, subordinate clauses are normally separated from the main clause by a comma.

Since dass sogar mein Bruder noch ein Stück nimmt is a subordinate clause, the comma is required:

• Das Brot ist so knusprig, dass ...

This is a standard punctuation rule in German.

German often uses the present tense in places where English might also use the present tense.

Here it can describe:

• a current situation
• a vivid observation
• a general kind of statement

So nimmt simply means takes in this structure.

Depending on context, English might translate it a little differently:

• that even my brother takes another piece
• that even my brother is taking another piece
• that even my brother will take another piece

But the German present tense itself is completely normal here.

Yes, often you can.

• sogar mein Bruder
• selbst mein Bruder

Both can mean even my brother.

However, sogar is especially common when emphasizing that something is surprising. In this sentence, sogar sounds very natural.

So:

• dass sogar mein Bruder noch ein Stück nimmt = very natural
• dass selbst mein Bruder noch ein Stück nimmt = also possible

German usually uses an article with nouns in many situations where English might also use one.

Here Das Brot means the bread. It refers to a specific bread, loaf, or bread being talked about.

Just Brot without an article is possible in some contexts, but it would usually sound more general or less natural here.

So:

• Das Brot ist so knusprig ... = this/the bread is so crispy ...

That fits the sentence best.