Heat 1 tablespoon of the oil in a large saucepan over high heat, add mushrooms and cook for 5 minutes stirring until softened.
Transfer to a heatproof bowl.
Heat 1 tablespoon of the remaining oil in the same pan and add onion and garlic and cook and stir for 5 minutes or until softened.
Add the flour and cook for 1 minutes or until well combined and then add stock, 2 cups of water and 2/3 of the cooked mushrooms and bring to the boil and then reduce heat and simmer for 10-15 minutes or until vegetables are tender.
Meanwhile heat the remaining oil in a small frying pan over moderately high heat and add the halloumi and sage and cook and turn for 2-3 minutes or until the haloumi is golden and then drain on paper towels.
Blend soup in batches or use a stick blender, return to the pot if done in a blender and add the cream and stir and cook for a further 5 minutes over a low heat or until heated through.
Ladle soup into serving bowls and top with reserved mushrooms, sage and halloumi.