melt in (someone's) mouth

Translations
таять во рту
The chocolate cake was so soft it just melted in my mouth.
Шоколадный торт был таким мягким, что просто таял у меня во рту.
Definitions
To be so tender or soft that it disintegrates or dissolves easily when placed in the mouth, often used to describe food that is exceptionally delicious and easy to eat.