Pre-heat the oven to 200°C and prepare a muffin tin (or use muffin cases).
Chop the courgette and onions and roast for around 20-25 minutes until they have softened and are browning. Remove and allow to cool.
Sift the flour and baking powder in a bowl, then add the dried rosemary and pepper.
In a separate bowl beat the egg and mix in the milk. Add in the onions, courgettes and feta cheese and stir until combined.
Very gently fold the wet ingredients into the flour mixture until everything has just combined (over-mixing will result in heavy muffins!)
Pour into the muffin cases or tin and sprinkle each one with sea salt. Bake for 17-20 minutes. Enjoy warm or cold!