Line a 23 cm x 13 cm (9 inch x 5 inch) loaf tin with baking paper and set aside.
Preheat the oven to 160℃ fan / 180℃ / 360℉.
Prepare the silverbeet - strip the leaves from the stalks, cutting the stalks into 1-2 cm (½ inch) pieces and roughly chopping the leaves.
Bring a small saucepan of water to the boil and add the stalks. Boil for 2 minutes then drain.
In a large frying pan, heat the olive oil over a medium heat then add the spring onions and fry for 1-2 minutes, before adding the garlic, silverbeet leaves and drained silverbeet stalks. Fry for 3-4 minutes, stirring occasionally, until the silverbeet has wilted. Take off the heat and leave to cool slightly.
In a large bowl, whisk the eggs with the flour and milk and season with salt and black pepper.
When the silverbeet is cool enough to handle, squeeze as much liquid out of it as you can, then place on a chopping board and roughly chop.
Add the chopped silverbeet to the egg, together with the grated cheese and chopped herbs. Crumble in the feta cheese, season with salt and black pepper, and stir to combine.
Pour into the lined tin then place in the preheated oven and bake for 30-35 minutes until golden and firm to the touch.
Cool in the tin for a few minutes before cutting into slices and serving warm or cold. It will be easier to slice after being left to cool.
Store any leftovers in the fridge.