Fill a kettle and boil it. Heat your oven to 180°C/Fan 160°C/Gas 4. Chop the potatoes so they are all equal sizes. Snap the woody ends off the asparagus stalks. Cut the asparagus stalks into thirds.
Half fill a pan with hot water from the kettle. Add the potatoes. Cook for 10-12 mins till the potatoes are tender. When the potatoes are cooked, add the asparagus to the pan and cook for another min. Drain and rinse under cold water.
Slice the potatoes so they're ½ cm thick. Trim and slice the spring onions. Finely slice the sorrel.
Break the eggs into a large bowl. Season with a little salt and pepper. Beat well. Add the spring onions, sorrel, potatoes and asparagus. Mix well.
Heat 1 tbsp olive oil in an ovenproof frying pan. Pour in the frittata mix. Cook over a low heat for 5-7 mins till the edges look cooked and crisp.
Transfer the frittata to the oven for 20-25 mins till golden and puffy. Pop a skewer in to the centre - if it comes out clean, it's ready.
Pop the spinach into a bowl. Finely slice the radishes and their leaves. Add to the spinach. Mix 1 tbsp of the vinegar with 1 tbsp olive oil. Season. Add the dressing to the bowl. Mix. Serve with wedges of frittata.