Toast bread cubes on a tray at 375 in oven. Saute garlic in 2 T each of butter and oil until the garlic is golden. When the bread cubes are crispy, toss with garlic butter and set aside. Saute leeks in remaining T each of butter and oil. After 1 minute, add mushrooms, herbs, salt, and pepper.
Cover the pan to retain the juices. The vegetables are ready when they are just tender. Pre-heat your oven to 375. Butter a 9x9 inch pan. Layer as follows; bread cubes, next cream cheese, next vegetables, and finally, grated cheese. Beat eggs and milk and pour over the other ingredients. Add salt and pepper, bake until frittata is puffy and golden, about 30 minutes.
Serve hot.