"In 'The Best Casserole Cookbook Ever' by Beatrice Ojakangas..."
INGREDIENTS
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1 tablespoon butter, plus extra for the dish
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4 plain croissants, split horizontally
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2 cups sliced mushrooms
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1/4 cup sliced green onion (white and green parts)
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4 large eggs
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1 cup milk
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1 cup shredded swiss cheese
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1 cup shredded mozzarella cheese
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1/4 cup grated parmesan cheese