Mushroom and thyme soup with roquefort croutons

Ingredients

• 20 gram dried porcini
• 100 millilitre boiling water
• 60 gram butter, coarsely chopped
• 70 millilitre olive oil
• 1 leek, thinly sliced
• 10 clove garlic, 2 finely chopped, and 8 bruised with the flat of a knife
• 750 gram portabello mushrooms, coarsely chopped
• 12 thyme sprigs, plus extra to serve
• 1 litre chicken stock
• 200 gram crème fraîche
• finely grated rind and juice ½ lemon
• 1/2 baguette, thinly sliced diagonally
• 300 gram any other variety of mushrooms, halved or quartered if large
• 1 teaspoon red wine vinegar
• roquefort or other blue cheese, to serve