Place the Jerusalem artichokes into a saucepan, with the garlic. Cover with water and bring to the boil. Reduce the heat and simmer for 8-10 minutes, or until tender, then drain. Leave to cool slightly.
Remove the bay leaf, then place the Jerusalem artichokes into a food processor with the butter, cream and lemon juice and blend to make a smooth purée.
Place the purée back into a saucepan, season to taste, with salt and lots of freshly ground black pepper and heat gently to warm through.