Bring the chicken or vegetable stock to the boil in a large, heavy-based pan over a medium heat.
Crush the garlic clove with the flat edge of a knife. Add the crushed clove to the stock. Add the thyme and season to taste with salt and freshly ground black pepper.
Bring the stock back to the boil and simmer for 2-3 minutes to allow the flavours to infuse. Remove the thyme and garlic and discard.
Add the polenta to the hot stock in a thin, steady stream. Stir immediately with a wooden spoon and continue stirring, as it cooks, for 2-3 minutes (or according to packet instructions). The polenta will thicken and have the texture of mashed potato when cooked.
Add the butter and stir thoroughly to combine.
Roughly chop the rocket leaves and add to the polenta.
Add the cubed Gorgonzola to the polenta and stir. Finally, add a squeeze of lemon juice and stir.
Serve on its own or as an accompaniment to roast chicken or grilled sausages.