Put the chicken stock, the lemon juice, rosemary sprigs and salt into a saucepan and bring to a simmer. Remove the sprigs
Slowly whisk in the polenta until it starts to thicken. Whisk in the butter. The polenta will take around 20 minutes to cook. As it thickens, swap the whisk for a wooden spoon. Should the polenta get too thick, add a little more stock
Once the polenta is cooked, cover with a sheet of greaseproof paper and place onto a clean tray. Leave in the fridge to cool until set, approximately 2 hours
For the second part of the polenta preparation, heat the stock first in a pan, then add 400g of the chilled polenta. Heat throughly, then add the crème fraiche, butter, lemon juice and Parmesan cheese. Mix thoroughly until smooth
Add the the salt and basil to the finished polenta, and serve immediately.