Pulse the mushrooms and lemon juice in a food processor until finely chopped. Melt the butter in a large saucepan over a moderate heat and sauté the shallots for 3-4 minutes, stirring occasionally. Add the mushrooms and bay leaf to the saucepan and cook for 15 minutes, stirring occasionally, until the liquid from the mushrooms has been released and then evaporated.
Cover with the chicken stock and bring to the boil. Reduce to a simmer and cook gently for 20 minutes. Remove from the heat and puree until smooth using a stick blender. Add the cream, bring back to the boil, then keep hot over a very low heat. Adjust the seasoning if necessary.
Combine the chopped herbs with the olive oil for the croutons. Melt the butter in an herb oil in a frying pan over a medium-high heat, then add the cubes of bread and sauté, tossing occasionally, for 3-4 minutes, until golden and crispy, making sure you season them as well. Ladle the hot soup into serving bowls and garnish with a few croutons. Serve immediately.
Freezing and defrosting guidelines
Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.