Heat butter in a medium saucepan over medium heat until melted. Add the garlic cloves, and cook until fragrant, about 1 minute.
Add the chopped onions, and saute the onions till they turn translucent.
Add the sliced mushrooms and cook them on medium heat until they are lightly browned and have released most of their water, about 8 – 10 minutes.
Remove 2 tablespoons of the mushrooms at this side, and set aside. This will be used as the garnish at the end.
Add the Italian herbs, salt, black pepper and vegetable stock to the mushrooms. Bring to a boil on medium heat, and then turn heat to low. Simmer uncovered for about 10 minutes. Turn off the heat.
Using an immersion blender or working in batches with a blender puree the soup until smooth. I prefer a little texture in this cream of mushroom soup, so I blitz it about 90%, leaving just a tiny bit of texture.
Return the mushroom soup to the saucepan and add cream as well as milk. Stir through, and heat the soup till it’s just warm, and then turn off the heat.
Garnish with reserved mushrooms and serve the cream of mushroom soup hot with garlic bread or croutons on the side.