Blanch peas until just tender (1-2 minutes). Drain, refresh and drain again. Set aside.
Heat 30ml oil in a 26cm-diameter (top measurement) non-stick frying pan over medium heat. Add onion and cook, stirring occasionally, until soft and golden (5-6 minutes). Add peas and cook, covered with a lid, over low heat until peas are tender (4-5 minutes). Transfer to a bowl and wipe out pan with absorbent paper.
Whisk 2 eggs in a bowl, add one-sixth each of parmesan and pea mixture, season to taste and stir to combine. Heat 15ml oil in a frying pan over medium high heat, add egg mixture and swirl pan to coat base evenly and cook until egg starts to set and turn golden around edges. Scatter over one-sixth of ricotta, tear some basil leaves on top and cook until frittata just starts to set and edges begin to turn golden (1-2 minutes). Slide onto a plate, invert back into pan, then cook until just cooked through (20-30 seconds). Transfer to a plate, wipe out pan and repeat with remaining ingredients. Serve frittatas with crusty white bread.
Rosa Mitchell, a great cook and friend of mine, taught me that frittatas could be cooked thin in a frying pan, whether or not you use fresh peas or frozen (both are good). I love them in a sandwich with prosciutto, rocket and parmesan, or you can use ingredients such as braised chicory or spinach.