Slice the leek and lightly fry in a pan with the olive oil for 7-8 minutes until lightly softened.
Section the florets from the broccoli and cauliflower, par boil for around 6 minutes in boiling water. Meanwhile make up the Colman’s Cheddar Cheese Sauce mix according to pack directions and stir in more milk to give the consistency you prefer. Add some Colman’s English Mustard and some salt and pepper if desired, to the mix.
Drain the vegetables and add to a dish along with the leeks, pour over half the cheese sauce, making sure it goes amongst all the veg, whiz the bread in a blender until you have a crumbly mix, scatter over the cheese sauce and pour the remaining mixture over the top.
Bake in a preheated oven for 20 minutes at 190°C, 180°C fan, Gas mark 5 or until brown and crispy on top.