Ég tæmi litla dós af tómötum út á pítsuna og bæti svo hveiti í deigið.

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

So litla dós simply means a small can or small can, depending on context. Icelandic often expresses indefiniteness with just the noun itself, sometimes helped by context or word order.

By contrast, the definite article is usually attached to the end of the noun:

• dós = a can / can
• dósin = the can

Those are the 1st person singular present tense forms:

• að tæma = to empty
• ég tæmi = I empty
• að bæta = to add / improve
• ég bæti = I add

So the sentence uses present tense:

• Ég tæmi ... = I empty ...
• ... og bæti ... = ... and add ...

This is a very common pattern with Icelandic verbs ending in -a in the infinitive.

Because litla agrees with dós in gender, number, and case.

• dós is feminine singular
• here it is the direct object of tæmi
• so it is in the accusative singular

The adjective lítill changes form to match:

• nominative feminine singular: lítil
• accusative feminine singular: litla

So:

• lítil dós = a small can as a subject
• ég tæmi litla dós = I empty a small can as an object

The preposition af normally takes the dative case.

So:

• tómatar = tomatoes (nominative plural)
• tómötum = tomatoes in the dative plural

In dós af tómötum, the phrase means a can of tomatoes.

This is a very common Icelandic structure:

• glas af vatni = a glass of water
• bolli af kaffi = a cup of coffee
• dós af tómötum = a can of tomatoes

Because út adds the idea of out or outward, so tæma ... út á means something like:

• empty out onto
• pour out onto

So:

• á pítsuna = onto the pizza
• út á pítsuna = out onto the pizza

It makes the action more vivid and complete: the contents are being emptied out from the can and onto the pizza.

Here á means onto, so it expresses movement toward a surface. With that meaning, á takes the accusative.

Also, pítsuna includes the suffixed definite article, so it means the pizza.

Breakdown:

• pítsa = pizza
• pítsuna = the pizza (accusative singular)

Compare:

• á pítsuna = onto the pizza (motion, accusative)
• á pítsunni = on the pizza (location, dative)

So the sentence uses pítsuna because something is being moved onto it.

Because the subject is understood from the first clause.

The full version could be:

• Ég tæmi ... og ég bæti svo hveiti í deigið.

But Icelandic, like English, often leaves out the repeated subject in coordinated clauses when it is obvious:

• I empty ... and add ...
• Ég tæmi ... og bæti ...

So the second ég is simply omitted because it would be repetitive.

Here svo means then.

In the second clause, the subject ég is omitted, so the finite verb bæti comes first in that clause, and svo follows it:

• og bæti svo hveiti í deigið

This is natural Icelandic word order.

In English, we often say:

• and then I add flour or
• and I then add flour

Icelandic often places the finite verb early, especially in main clauses.

The preposition í can take either:

• accusative for movement/change into something
• dative for location inside something

Here the flour is being added into the dough, so Icelandic uses the accusative:

• í deigið = into the dough

Compare:

• hveiti í deigið = flour going into the dough
• hveiti í deiginu = flour in the dough

So this is the same kind of contrast as:

• á pítsuna = onto the pizza
• á pítsunni = on the pizza

Deigið is accusative singular neuter definite.

Breakdown:

• deig = dough
• deigið = the dough

Because í here expresses motion/change into something, it takes the accusative, and for a neuter noun like deig, the nominative and accusative singular look the same in the definite form:

• nominative: deigið
• accusative: deigið

So the form does not change, even though the case matters grammatically.

Hveiti is the direct object of bæti, so it is in the accusative.

However, hveiti is a neuter mass noun, and its nominative and accusative singular have the same form:

• nominative: hveiti
• accusative: hveiti

So you do not see a visible change.

This is very common with neuter nouns in Icelandic.

Here bæta means to add.

A very common pattern is:

• bæta einhverju í eitthvað or
• bæta eitthvað í eitthvað

In this sentence:

• bæti hveiti í deigið = add flour to the dough

Be careful, because bæta can also mean improve in other contexts:

• bæta íslenskuna sína = improve one’s Icelandic

So the exact meaning depends on context.

Because the speaker is referring to specific things already understood in the situation: the pizza and the dough.

In recipe or cooking language, Icelandic often uses the definite form when the item is the one currently being worked on:

• á pítsuna = onto the pizza
• í deigið = into the dough

If you made them indefinite, the meaning would be more general or less specific.

So this sounds like someone describing concrete steps in preparing a particular pizza and a particular batch of dough.