Beat eggs. Grate cheese. Remove crust from bread and discard. Cut bread into 1/2" squares. An easy way is to stack the bread slices then cut through all of them at one time.
Heat milk. Add eggs, bread, cheese and bacon/onion, if desired. Pour into greased baking dish or 8 x 8" cake pan. Refrigerate several hours or overnight. Bake at 325 for about 30 minutes or until custard is set. Don't over cook. Note: When doubling this recipe for a crowd, a 9 x 13" dish is just right. Allow 10 to 15 minutes extra cooking time.