Place the carrots and leek in a large steamer and cook for 3 minutes. Add the cauliflower and broccoli and continue to steam for 6 minutes. Finally add the spinach and give it another minute or two to just wilt down.
Tip the steamed vegetables into a shallow baking dish and spread out evenly.
Whisk a little of the milk into the cornflour until smooth and then whisk in the remainder, then stir in two-thirds of the cheese. Season with salt and pepper and pour over the vegetables.
Spread the slices of soda bread with butter and break into large chunks, then scatter over the vegetable mixture in an even layer. Sprinkle the rest of the cheese on top and then bake for 25-30 minutes until the crumble is bubbling and golden. Serve straight to the table.