Preheat the oven to 180ºC and grease a 12-cup shallow muffin or scone tin.
Beat the eggs with the garlic and season with salt and pepper. Add the cayenne, if used, then set aside.
Divide the feta, spring onion, peas and mint between the muffin cups then spoon over the egg mixture. (Note: don’t fill the cups completely, otherwise the frittatas will look like puffed-up muffins)
Bake for approx. 15 minutes until golden. Leave them to cool in the tin then transfer to a plate.
Serve warm or at room temperature.