The correct answers are The chef makes an amazing mushroom soup. and I always enjoy the atmosphere at this lovely restaurant.

We use an before words that start with a vowel sound (like amazing).

We use the when talking about a specific, unique thing in a certain context (like the atmosphere of a specific restaurant).

Many learners forget to include articles entirely, but in English, singular countable nouns and specific uncountable nouns usually need a little helper word in front of them!