Chop up all the root veg, any leeks and tougher stems of spinach and put on the pan to boil. You can add spinach leaves to wilt when it has cooked a little. The aim here is to just soften the veg, not to boil it to a mush.
Chop up any garlic, onion, celery, courgettes and mushrooms and saute in a little olive oil.
When the veg is softened drain the root veg and pour into a baking dish. Add the fried veg and mix up.
To make the white sauce put the milk, 50g plain flour and 50g butter into a pan. I used the one I fried the veg in. Whisk as the mixture comes to a boil and keep whisking until it has thickened.
If you are using any cheese add it to the veg mixture.
Then pour over the white sauce. You might want to add mustard or salt or pepper or all of these things.
To make the crumble mix the flours and the olive oil with your hands.
You are aiming to get a nice crumbly mix. If you have any herbs, hard cheese, chopped nuts or seeds you can add them too.
Sprinkle the crumble mix over the veg. You can use the remaining butter to dot onto the top of the crumble mix. Bake for around 45 minutes. The top should be golden brown and the vegetables cooked through.