In a large saucepan, bring the stock to the boil. Slowly pour in the polenta, a little at a time, until completely absorbed. Lower the heat, stir quickly for 5 mins, then remove from the heat altogether. Stir in 1 tbsp of the Parmesan, then spread the polenta out on a large parchment-lined baking sheet, so that its 2-3cm thick.
Cook the broccoli in salted water for 2 mins, drain, then rinse under cold water.
Sprinkle the mozzarella and remaining Parmesan over the polenta, then top with the tomatoes, garlic, broccoli and sausage.
Bake for 20 mins until the sausage is browned and the sides of the polenta crisp.
