Cook the peas in salted water with the onion, mint and garni until soft.
Remove the mint, garni and onion.
Pass firmly through a sieve.
Add to the bechamel, reboil and simmer for 5 min correct the seasoning.
Pass through a strainer.
Return to a clean pan, reboil, skim, correct the seasoning and consistency.
Finally stir in the cream.
Serve with croutons.