Grate the Parmesan. Zest the lemons. Snap off any tough stalks of the asparagus spears.
- 1 Heat oven to 220°C/200°C fan/gas 7.
- 2 Bring the milk and stock to the boil in a pan over a medium-high heat.
- 3 Add the polenta in a steady stream, while whisking.
- 4 Keep whisking for 1 min, reduce the heat to low and cook for 35-45 mins, stirring frequently.
- 5 Stir in the butter, Parmesan and lemon zest. Season to taste.
- 6 Meanwhile, place the prosciutto on a lined baking tray and bake for 10 mins, turning once. Set aside.
- 7 Heat the oil in a griddle or frying pan over a medium-high heat. Cook the asparagus, turning, for 3-4 mins.
- 8 To serve, top the polenta with asparagus, pieces of prosciutto and some extra grated Parmesan.