Bring the measurement water to the boil in a large heavy-based saucepan. Put the polenta in a jug and pour into the water in a slow but steady stream, stirring vigorously with a wooden spoon to prevent any lumps forming. Reduce the heat to a gentle simmer and cook, stirring continuously, for about 5 minutes or until the polenta is thick and comes away from the side of the pan. Season with salt and pepper.
Pour the polenta into a greased baking dish about 25 x 18 cm (10 x 7 inches). Blanch the asparagus in a saucepan of boiling water for 1–2 minutes or until just tender. Drain well. Top the polenta with a layer of ham, then the asparagus and lastly a layer of fontina and Parmesan.
Cook under a preheated very hot grill, about 7 cm (3 inches) from the heat, until crisp and golden. Scatter basil leaves over the top, cut into wedges and serve immediately.