Slice and cook the bacon on medium heat. Remove the bacon from the heat and place on a plate covered by paper towels to drain the extra bacon grease.
Heat up oil on the stove. Slice half of an onion into very thin straws. Whisk an egg and coat the onions in the egg. Transfer the onions from the egg to the cornstarch and coat. Add the onions to the oil and fry until crisp and brown. Remove from the oil and season with salt.
Bring a pot of water to a boil. Add the green beans in the water and season the water with salt. Let the green beans boil for 7-10 minutes. Strain out the water.
Add the green beans to a bowl. Add in the mayonnaise, sour cream, freshly grated parmesan, garlic, salt and pepper. Mix until well combined. Transfer the green bean mixture to a casserole dish. Top with a little extra freshly grated parmesan.
Bake for 18-20 minutes. Top with bacon and crispy onions and serve warm.
Notes
-save leftovers in an airtight container or covered with aluminum foil or plastic wrap in the refrigerator for up to 5 days.-freeze leftovers in a freezer safe container for up to 2 months.