אתמול בחרנו מתכון פשוט לעוגה, כי לא היה לנו הרבה זמן.

No. אתמול is one complete word meaning yesterday. It just happens to begin with the letters את.

So:

• אתמול = yesterday
• את = the marker used before a definite direct object

They are different words.

This also helps explain why there is no separate את before מתכון: מתכון here is indefinite (a recipe), so Hebrew does not use the direct-object marker there.

Hebrew often puts a time word or phrase near the beginning of the sentence, especially to set the scene.

So starting with אתמול is very natural and means something like:

• Yesterday, we chose...

Hebrew word order is fairly flexible. You could also say:

• בחרנו אתמול...

but אתמול בחרנו... sounds very normal and gives the time frame first.

בחרנו means we chose.

It comes from the verb לבחור = to choose.

In the past tense, Hebrew adds endings to show who did the action. Here:

• בחר- = the past-tense stem
• -נו = we

So:

• בחרתי = I chose
• בחרת = you chose
• בחרנו = we chose

Hebrew does not have an indefinite article like English a/an.

So:

• מתכון can mean a recipe
• עוגה can mean a cake

If Hebrew wants to say the, it usually adds ה־:

• מתכון = a recipe
• המתכון = the recipe

That is why מתכון פשוט לעוגה naturally means a simple recipe for a cake even though there is no separate word for a.

In Hebrew, adjectives usually come after the noun they describe.

So:

• מתכון פשוט = recipe simple = a simple recipe

This is the normal order in Hebrew.

Also, the adjective must agree with the noun in:

• gender
• number
• definiteness

Here, מתכון is:

• masculine
• singular
• indefinite

So the adjective is also masculine, singular, and indefinite:

• פשוט

For comparison:

• המתכון הפשוט = the simple recipe

לעוגה is made of:

• ל־ = to / for
• עוגה = cake

So literally it means for a cake.

In this sentence, מתכון לעוגה means:

• a recipe for a cake
• or more naturally in English, a cake recipe

The preposition ל־ is very commonly used this way after מתכון.

כי means because in this sentence.

It introduces the reason:

• כי לא היה לנו הרבה זמן
• because we didn’t have much time

Be aware that כי can sometimes mean that in other sentences, depending on context. But here the meaning is clearly because.

Literally, לא היה לנו is something like:

• there was not to us

Hebrew often expresses to have with a structure based on there is / there was plus ל־ (to someone).

So:

• יש לנו = we have
  literally: there is to us
• היה לנו = we had
  literally: there was to us
• לא היה לנו = we didn’t have

This is a very important Hebrew pattern.

Because the thing being talked about is זמן (time), and זמן is singular.

So Hebrew uses singular היה:

• לא היה לנו הרבה זמן
• we didn’t have much time

Even though English uses we, the verb here is not agreeing with we. It is agreeing with the thing that existed or did not exist — in this case, זמן.

Compare:

• לא היה לנו זמן = we didn’t have time
• לא היו לנו שעות = we didn’t have hours

Since שעות is plural, that second sentence uses היו.

הרבה means much, many, or a lot of, depending on context.

So:

• הרבה זמן = much time / a lot of time

This is a very common and natural phrase in Hebrew.

A useful point:

• with countable nouns, הרבה can mean many
• with uncountable nouns like זמן, it means much / a lot of

So:

• הרבה ספרים = many books
• הרבה זמן = much time

Yes. That is a very natural English translation.

Word-for-word, מתכון פשוט לעוגה is:

• a simple recipe for a cake

But in smoother English, people often say:

• a simple cake recipe

Both are good ways to understand the Hebrew.

So the Hebrew structure is one thing, and the most natural English translation may be a little different.