Preheat oven to 350 degrees F (175 degrees C). Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Drain, crumble and set aside.
Place eggs in a saucepan and cover with cold water. Bring water to a boil and immediately remove from heat. Cover and let eggs stand in hot water for 10 to 12 minutes. Remove from hot water, cool, peel and chop.
Lightly grease a 2 quart casserole dish. Sprinkle half of the chopped egg in the bottom of the casserole, add half of the bacon; repeat.
Melt butter in a medium saucepan over medium heat. Add onion and cook until softened and transparent. Stir in flour. Slowly add milk and shredded cheese. Stir until cheese is melted and sauce is smooth and creamy. Pour over layered eggs and bacon.
