Learn Hardcore Portuguese (Portugal): Põe pimenta na sopa, mas não demasiado sal. - Put pepper in the soup, but not too much salt.

Yes. In European Portuguese, põe is the affirmative imperative for tu (informal you). It comes from the present indicative tu pões; drop the final -s to get the imperative: põe. Formal you: ponha (você). Plural you: ponham (vocês). For emphasis you can say põe tu, not tu põe.

Why is there no verb in the second part, mas não demasiado sal?

It’s ellipsis. The full form would be:

mas não ponhas demasiado sal (if addressing tu)
mas não ponha demasiado sal (if addressing você) Negative imperatives use the present subjunctive in Portuguese. Omitting the repeated verb is very natural.

Why na sopa instead of à sopa or no sopa?

na = em + a (“in/on the”) with a feminine noun (a sopa).
With pôr, the usual preposition is em: pôr X na sopa/na mesa/no prato.
à (“to the”) is used with verbs like adicionar: adicionar sal à sopa.
no is for masculine nouns: no prato. Since sopa is feminine, it’s na sopa.

In Portugal, does pimenta mean black pepper or chili?

In Portugal, pimenta is typically black pepper (ground or grains). Chili pepper is malagueta or piripíri, and bell pepper is pimento. In Brazil, pimenta often means chili; black pepper is pimenta‑do‑reino.

What is demasiado doing here—does it agree with the noun?

Here demasiado acts like a determiner meaning “too much” before a noun, so it agrees:

demasiado sal (masc. sing.)
demasiada água (fem. sing.)
demasiados problemas (masc. pl.)
demasiadas pessoas (fem. pl.) When it modifies adjectives/adverbs, it stays invariable: demasiado caro/rápido.

Can I say mas não muito sal instead of mas não demasiado sal?

You can, but the meaning is softer:

não muito sal = “not much salt.”
não demasiado sal = “not too much salt” (avoid exceeding a reasonable amount).

Other ways to say “too much salt” in European Portuguese?

sal a mais (very common)
sal demais (also heard; more informal)
With a verb: pôr sal a mais / pôr sal demais Before a noun, demasiado sal or sal a mais are the most natural.

Is the comma before mas necessary?

Standard usage puts a comma before mas when introducing contrast, so ..., mas ... is recommended. You may see it omitted in short sentences, but the comma is the norm.

Any quick pronunciation tips for the tricky words?

põe: nasal vowel; roughly “poyn,” not “poe.”
mas: in European Portuguese, final s before a consonant sounds like “sh”: mas não ≈ “mash não.”
não: nasal diphthong, like “now” but nasal.
pimenta: stress the middle syllable: pi-MEN-ta.
sopa: SOH-puh (final -a is like a short “uh” in EP).
demasiado: de-ma-si-A-do (stress on “A”).

Why does põe have a tilde, and why is the infinitive pôr written with a circumflex?

The tilde in põe marks a nasal vowel and the stressed syllable. The infinitive pôr has a circumflex to distinguish it from the preposition por (“by/through”) and to mark vowel quality. So: pôr (to put) vs por (by/through).

Could I use meter instead of pôr?

Yes. In Portugal, meter is very common in everyday speech: Mete pimenta na sopa, mas não demasiado sal. Pôr is neutral and works in all registers; meter is more colloquial.

How can I avoid repeating sopa (e.g., “Put some pepper in it…”)?

Use the indirect clitic for “to it”:

Põe-lhe pimenta, mas não demasiado sal. For a full negative clause you can say:
..., mas não lhe ponhas demasiado sal (tu)
..., mas não lhe ponha demasiado sal (você)

What are the forms if I’m talking to more than one person?

Plural you (vocês): Ponham pimenta na sopa, mas não demasiado sal. Negative: Não ponham...
Old-fashioned vós: Ponde pimenta... (rare in modern speech).

Why is there no article before pimenta or sal? How do I say “some pepper”?

With mass nouns, Portuguese often omits the article in instructions. To make “some” explicit, use a quantifier:

um pouco de pimenta (a little/some pepper)
um bocadinho de sal (a tiny bit of salt) Avoid um sal/uma pimenta here; they don’t mean “some.”

Can I use a pronoun like põe-no for “put it”?

With affirmative imperatives, object pronouns attach after the verb with a hyphen. After forms ending in nasal sounds like põe, the masculine direct object o becomes no: põe-no (“put it”). Feminine would be põe-na. In the given sentence, pronouns aren’t needed because the nouns (pimenta, sal) are explicit.