1.Squeeze the sausage meat from casings. Heat oil in a 26cm (top measurement) 21cm (base measurement) non-stick frying pan over medium heat; cook sausage meat, breaking it up into smaller pieces with a wooden spoon, until browned lightly. Remove from pan with a slotted spoon; drain on paper towel.
2.Add potato and onion to pan; cook, stirring occasionally, for 7 minutes or until onion is soft. Add the water; bring to the boil. Reduce heat; simmer, uncovered, for 8 minutes or until water is absorbed and potato is tender. Return sausage to pan.
3.Combine eggs, milk and ½ cup of the parmesan in a large jug or bowl; season well. Pour egg mixture into pan. Reduce heat to low; add asparagus, pushing into the egg mixture. Cook, covered, for 5 minutes or until almost set.
4.Preheat grill (broiler) on medium-high heat. Grill frittata for 2 minutes or until set and golden. (If the handle of the pan is not heatproof, wrap it in several layers of foil and keep it away from the direct heat.) Top frittata with remaining parmesan. Serve with toasted bread.
Frittata can be made ahead of time and reheated until warm.Recipe is not suitable to freeze.