Preheat the oven to 180 C.
Whisk together the eggs, milk, Worcestershire sauce, pepper and salt in a bowl. Roughly cut each slice of bread into 6 pieces. Dunk the bread in the egg mixture. Let it sit until you need it (see notes).
Heat a large wide pan over medium heat. Sauté the leeks and garlic in a little butter or oil until they cook down and lightly brown around the edges.
Turn the heat up to high. Add the mushrooms to the pan and get some colour on them. If they leach out too much water continue cooking until they dry out. Add the corn and cook for 2-3 mins.
Assemble in layers: tip half the soaked bread evenly into an oven-proof dish. Top with half the amount of the vegetable mixture. Add half the amount of cheese. Repeat in the same order one more time.
Cover the dish with foil and bake for 25 mins. Bake uncovered for a further 10 mins until the cheese melts through. Top with chopped basil and serve immediately.