Chop the garlic, carrots, celery, and onion and add them to a pan along with half of the butter. Cook on a low heat for about 5-10 minutes.
When the veg is beginning to soften, but not colour, add the lentils and stock. Turn the heat up to medium. Cook for about 15 minutes until the veg and the lentils are soft. Stir occasionally.
Remove from the heat and add the sorrel, remainder of the butter and the cream. Using a stick blender, blend until it is a smooth liquid.
Add more liquid if it is not to the desired consistency, and pop it back on the heat until it's piping hot. Season as necessary.
Serve up and add a little drizzle of cream if you want to look swanky.