Peel and/or trim the vegetables, cut them into large, even chunks, then boil in salted water or steam until tender. If you are including shredded curly kale and/or chard, wilt it in a hot pan instead. Be careful not to overcook the veg, because they will be cooked again in the oven.
Make a bechamel by melting the butter in a small pan, adding the flour and stirring until it forms a thick paste. Whisk in the milk and cook, stirring, until the consistency is smooth and dense, then season with salt and nutmeg.
Mash, or roughly break up the vegetables with a small knife, then stir in the bechamel, eggs and cheese, and mix well.
Butter and either flour or breadcrumb a standard 23cm x 33cm rectangular pan, then tip in the mixture. Bake in a 180C (160C fan)/350F/gas 4 oven for 25 minutes, until set firm and just starting to get some colour on top.
Leave to cool slightly before cutting into squares and serving.
