Learn Hardcore Norwegian: Kremen blir tykkere når kokken tilsetter sukker i gryten. - The cream becomes thicker when the chef adds sugar to the stew.

Use of når indicates a temporal condition that regularly happens or expresses a general truth: whenever the cook adds sugar, the cream becomes thicker. hvis would introduce a hypothetical or conditional situation—if the cook adds sugar (implying it might not happen). Since this sentence describes what always happens, you use når.

When would you use da instead of når?

da is used for a single event in the past. If you refer to one specific occasion when the cook added sugar and the cream got thicker, you would choose da and switch to past tense:
Kremen ble tykkere da kokken tilsatte sukker i gryten.

Why does the verb come after the subject in the clause after når? Why do we not say når tilsetter kokken sukker i gryten?

In Norwegian subordinate clauses introduced by conjunctions like når, the word order is subject–verb–object (SVO). The main-clause verb-second (V2) rule does not apply here. That is why you keep når + subject + verb.

How would the word order change if you placed the time clause first?

If you start with the time clause, the main clause must invert subject and verb (V2) after the comma. For example:
Når kokken tilsetter sukker i gryten, blir kremen tykkere.

Why is blir used here instead of er?

bli plus an adjective expresses a change of state: the cream becomes thicker. Saying er tykkere would simply state a static property (is thicker) without emphasizing the thickening process.

Why are kremen and gryten in the definite form?

Definite forms (ending with -en) mark known or specific items. Here the sentence refers to a particular cream (the one in question) and a specific pot (the cook’s pot). If you spoke of any cream or any pot in general, you would say en krem or en gryte.

Why is there no article before sukker?

sukker is an uncountable mass noun in Norwegian, just like in English. You do not use a definite or indefinite article when speaking of the substance in general. To specify an amount you could say noe sukker (some sugar) or et kilo sukker (a kilo of sugar).

How do you form the comparative tykkere?

For most one-syllable adjectives you form the comparative by adding -ere to the root. tykk (thick) becomes tykkere (thicker). Multi-syllable adjectives typically take mer + adjective instead.

What is the difference between tilsette and sette?

sette means to place or put something somewhere. tilsette specifically means to add an ingredient (in cooking, chemistry, etc.). tilsette is an inseparable verb—you cannot split it into sette and til in this context.

How would you express the same idea in the past tense?

Replace present blir with past ble, tilsetter with tilsatte, and use da for the time clause:
Kremen ble tykkere da kokken tilsatte sukker i gryten.

Should there be a comma before når?

In modern Norwegian punctuation, commas before subordinate clauses are optional. Some formal texts include a comma to clarify clause boundaries (for example Kremen blir tykkere, når kokken tilsetter sukker i gryten), but in everyday writing it is often omitted.