Learn Hardcore German: Als Dessert essen wir Eis, und alle sind entspannt und glücklich. - As dessert we eat ice cream, and everyone is relaxed and happy.

als + noun is often used to say that something is used/serves as something:
- Ich arbeite als Lehrer. – I work as a teacher.
- Wir nehmen Obst als Vorspeise. – We have fruit as a starter.

Other options are also possible, with slightly different nuances:

zum Dessert – very common; literally for dessert, idiomatic in menus and everyday talk.
für das Dessert – possible, but less idiomatic in this context; sounds more like “for the dessert course” in a planning sense.

So:

Als Dessert essen wir Eis. – We eat ice cream as dessert.
Zum Dessert essen wir Eis. – We eat ice cream for dessert.

Both are correct; als Dessert highlights the role of the ice cream, zum Dessert is the most common everyday phrasing.

Why is the verb before the subject: essen wir instead of wir essen?

German main clauses normally have the finite verb in second position (V2 rule), but “second” means second element, not second word.

The fronted element is Als Dessert (one element, even though it has two words).
The verb essen must therefore come next (second position).
The subject wir comes after the verb.

So:

Wir essen Eis. – Subject first → wir (1st), essen (2nd).
Als Dessert essen wir Eis. – Fronted phrase first → Als Dessert (1st), essen (2nd), wir (3rd).

This word order (fronted phrase + verb + subject) is extremely common and natural in German.

Is Dessert in a special case here? Why is it just Dessert and not something like dem Dessert?

In Als Dessert essen wir Eis, Dessert is in the nominative after als.

When als means as in the sense of “in the role of / functioning as”, it is followed by a bare noun phrase in the nominative:

Er arbeitet als Arzt. – as a doctor (nominative)
Sie benutzt den Schal als Decke. – as a blanket (Decke is nominative here)
Als Dessert essen wir Eis. – as dessert (Dessert is nominative)

So:

No article is needed after this kind of als.
The case is nominative, not dative or accusative.

Why is Eis used without an article? Why not ein Eis or das Eis?

Eis here behaves like a mass noun (ice cream in general), not a countable unit (an ice cream).

Wir essen Eis. – We eat ice cream (in general, some amount of ice cream).
Wir essen ein Eis. – We eat an ice cream (one portion, one cone/cup).
Wir essen das Eis. – We eat the ice cream (a specific ice cream already known in the context).

In the sentence Als Dessert essen wir Eis, the focus is on what is served as dessert (ice cream as a type of dessert), not on counting portions, so the article-less mass noun is natural.

Why is there a comma before und? Is that required in German?

In Als Dessert essen wir Eis, und alle sind entspannt und glücklich, there are two independent main clauses:

Als Dessert essen wir Eis.
Alle sind entspannt und glücklich.

They are joined by und.

In standard modern German:

A comma between main clauses with und/oder is generally optional, as long as they share no common parts.
It may be used to make the sentence clearer or to emphasize the separation.

So both are correct:

Als Dessert essen wir Eis und alle sind entspannt und glücklich.
Als Dessert essen wir Eis, und alle sind entspannt und glücklich.

School grammars often prefer omitting that comma, but it is not wrong to include it here.

What does alle refer to, and why does the verb sind have to be plural?

Alle means everyone / all (of us/them) and is grammatically plural, so the verb must also be plural:

alle sind entspannt und glücklich – everyone is relaxed and happy.

Possible references of alle depend on context:

It might mean all the people at the table.
Often, in a context like this, it effectively means we all:
- Als Dessert essen wir Eis, und alle sind entspannt und glücklich.
  ≈ As dessert we eat ice cream, and we’re all relaxed and happy.

Because alle is plural, you need sind, not ist:

Alle sind da. – Everyone is here.
Er ist da. – He is here.

Why do entspannt and glücklich have no endings? Shouldn’t there be something like entspannte or glückliche?

Adjectives in German only take endings when they directly modify a noun:

die entspannte Familie – the relaxed family
ein glücklicher Mann – a happy man

But in the sentence alle sind entspannt und glücklich, the adjectives are predicate adjectives after the verb sein. Predicate adjectives in German do not take endings:

Ich bin müde. – I am tired.
Sie ist glücklich. – She is happy.
Wir sind zufrieden. – We are satisfied.
Alle sind entspannt und glücklich. – Everyone is relaxed and happy.

So entspannt and glücklich are in their base form here, which is correct.

Is Als here the same als that introduces time clauses, like als ich klein war?

It is the same word als, but used in a different function.

Als as a subordinating conjunction (time, “when” in the past):
- Als ich klein war, spielte ich viel draußen. – When I was little, I played outside a lot.
Als as a preposition-like word meaning “as” (role/function):
- Er arbeitet als Lehrer. – He works as a teacher.
- Wir benutzen das Zimmer als Büro. – We use the room as an office.
- Als Dessert essen wir Eis. – We eat ice cream as dessert.

In your sentence, als is not a conjunction introducing a clause; it introduces a role: ice cream in the role of dessert.

Why is it Als Dessert and not Wie Dessert? In English we say “like dessert”.

For as / like comparisons, German distinguishes between als and wie:

als = as (in the role of / in comparison where things are not equal)
wie = like / as … as (when things are equal or similar)

But here, als is not a comparison at all; it means as in the sense of a role/function:

Als Dessert essen wir Eis. – We eat ice cream as dessert.
Er arbeitet als Koch. – He works as a cook.

You would not say:

✗ Wie Dessert essen wir Eis. – incorrect in this meaning.

Use wie instead in true equality/similarity comparisons:

Er isst wie ein Kind. – He eats like a child.
Sie singt wie ein Profi. – She sings like a pro.

Could the present tense essen wir and sind also refer to the future, like a plan?

Yes. German Präsens (present tense) often covers future meaning if context makes it clear:

Morgen essen wir Eis. – We’re eating ice cream tomorrow / we’ll eat ice cream tomorrow.
Nächste Woche fahren wir nach Berlin. – Next week we’re going to Berlin / we’ll go to Berlin.

Your sentence, without extra context, is present by default:

Als Dessert essen wir Eis, und alle sind entspannt und glücklich.
– As dessert we (usually/now) eat ice cream, and everyone is relaxed and happy.

But in the right context (e.g. describing a planned menu), it can be understood as a plan for later.

To be explicitly future, you could say:

Als Dessert werden wir Eis essen. – As dessert we will eat ice cream.
Dann werden alle entspannt und glücklich sein. – Then everyone will be relaxed and happy.

What is the gender and plural of Dessert and Eis, and does that matter in this sentence?

das Dessert (neuter), plural: die Desserts
das Eis (neuter), usually uncountable as ice cream; plural die Eis is rare and mostly used in specific contexts (e.g. different kinds of ice creams).

In the sentence:

Als Dessert – no article, so you don’t see the gender, but it is neuter.
Eis – used as a mass noun, so again no article.

The gender doesn’t change the form of the sentence here, but it’s useful to know for other contexts:

Das Dessert ist lecker.
Das Eis schmeckt gut.

Why is it und alle sind entspannt und glücklich instead of using a reflexive verb like fühlen sich?

German allows both sein + Adjektiv and sich fühlen + Adjektiv to talk about feelings or states, with slightly different nuances:

alle sind entspannt und glücklich
– everyone is relaxed and happy (a state, description)
alle fühlen sich entspannt und glücklich
– everyone feels relaxed and happy (more explicitly subjective feeling)

Both are correct; your sentence uses sein, which is very common and perfectly idiomatic for describing how people are after dessert.