Heat the oven to 220C/200C fan/gas 7. Butter a 900g loaf tin and line with a wide strip of baking parchment. Mix the flour, polenta and baking powder in a bowl with 1 tsp of salt.
Whisk the eggs, milk and melted butter in a jug. Pour into the dry ingredients and mix together. Stir in the cheese and courgettes. It will be quite runny at this stage but don’t worry, as the polenta gradually swells and soaks up the liquid in the oven.
Pour into the prepared loaf tin and bake for 15 mins, then turn the oven down to 200C/180C fan/gas 6 and cook for another 25-30 mins or until a skewer inserted in the middle of the loaf comes out clean (you can cover the top loosely with foil if starts to get dark too quickly).
Leave to cool completely in the tin, then turn out and slice.