Melt 150 g butter in a heavy-based saucepan and sweat the shallots for 5 minutes without colouring. Add the fennel and continue to sweat over a low heat for a further 10–15 minutes without colouring until the fennel is tender. Pour in the Pernod and reduce until it has evaporated. Add the chicken stock and reduce by half. Add the cream and reduce by half. Blend to a purée in a food processor and emulsify with the chilled butter. Season with salt and freshly ground pepper and pass the fennel purée through a fine sieve.