Heat 2 tablespoons oil in a large saucepan over medium heat. Add onion, chilli and ginger. Cook, stirring occasionally, for 5 minutes, or until soft. Add flat mushrooms. Cook, stirring occasionally, over a high heat for about 8 minutes, or until mushrooms are tender.
Sprinkle flour over mushrooms. Cook, stirring for 2 minutes. Remove the pan from heat. Gradually add stock, stirring constantly. Add bay leaves. Return the pan to a medium-high heat. Bring to the boil. Simmer, uncovered, stirring occasionally, over medium-low heat for about 10 minutes, or until thickened slightly. Remove from the heat. Remove and discard bay leaves. Cool slightly.
Blend until smooth. Return to same saucepan. Meanwhile, heat remaining oil in a large frying pan over a high heat. Add cup mushrooms. Cook, stirring occasionally for 4 minutes or until tender. Add kale. Stir until wilted. Add mushroom mixture to soup, then stir in cream if using. Stir over low heat until combined. Season. Serve with toasted sourdough bread.