オーブントースターのタイマーが鳴る。食パンがコンガリ焼けた、香ばしい匂い。

。、。

The oven toaster timer goes off. The toast is perfectly browned — a fragrant smell.

Literal

Oven-toaster [gen-の] timer [subj-が] rings. Toast [subj-が] golden-browned baked, fragrant smell.

コンガリ is a mimetic for food browned to a golden, crispy finish. 香ばしい (こうばしい) 'fragrant / savory-smelling' specifically describes the pleasant aroma of toasted or roasted food. The second sentence is a verbless fragment — pure sensory description. This sentence pair reads like prose fiction or a screenplay stage direction.