Calcium deposits inside of the inner egg shell.

[Kberly]

My Cream legbar is laying eggs with little bumpy packets of calcium granules both on the outside of the shell and on the inside. I am finding them actually embedded several mm into the egg white when I boil an egg.
I can’t continue to use these eggs for cooking as it is a very unpleasant experience to bite into calcium when expecting a nice creamy egg.

 

[Perris]

If she was laying normal eggs before, it is caused by too much calcium in her diet.
If she is a new layer, it will probably sort itself out as her system gets going; all sorts of oddities can happen at the start of a hen's laying period.
If she has always laid eggs like this and everyone else in the flock lays normal eggs, it may be a defective shell gland and there's no fix.

Until it's fixed, you could break her eggs into a ramekin or suchlike and scoop out any calcium granules, to avoid wasting the whole egg.