Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the butter, spring onions and courgette in a saucepan or in a bowl in the microwave until the butter has melted.
Line the slow cooker pot with nonstick baking paper, tip in the courgette and butter mix, then add the broad beans. Fork together the eggs, crème fraîche, herbs and a little salt and pepper in a bowl, then pour into the pot. Cover with the lid and cook on high for 1½–2 hours or until set in the middle.
Lift the pot out of the housing using oven gloves. Loosen the edge of the frittata with a knife, carefully turn out on to a large plate and peel off the lining paper. Cut the frittata into wedges and serve with salad and spoonfuls of Beetroot Chutney (see