Once it boils, lower the heat and let the soup simmer for twenty minutes.
煮开后把火调小,让汤小火慢炖二十分钟。
Keep the sauce on a gentle simmer so it thickens without burning.
让酱汁保持小火微滚,这样会变浓稠又不会烧焦。
"simmer"=小火微滚,只有小气泡冒出(接近沸点),比大火 "boil"(滚开)更温和,适合炖菜和酱汁。