Preheat oven to 400.
Toast breadcrumbs on a baking sheet until golden, about 4 minutes. Let cool, then mix with melted butter, cheddar cheese and parsley. Cook bacon until crispy, then let cool and chop into small pieces and add to the breadcrumb mixture.
Melt butter in a medium sauce pot over medium heat and whisk in flour to create a roux. Let the roux cook for 3 minutes, whisking constantly.
Add in milk and bring to a boil, then simmer.
Whisk in cream, mustard, worcestershire, nutmeg, cheese, salt, and pepper until smooth.
Slice onions thinly. Add to a large frying pan with butter and cook over medium heat. Stir occasionally and cook until the onions brown.
Cook noodles in a pot of well salted water until al dente. Drain and transfer to a mixing bowl.
Combine sauce, noodles and onions in a large mixing bowl. Pour into a baking dish.
Cover noodles with topping and bake at 375 for 20 minutes. Let cool, then enjoy!