Oldschool there are two issues involved.
1. Whether or not your instructions and explanations constituted a significant literary expression. If not, the recipes are not copyrightable in the first place. An IP judge would have to make that decision. Your certified letter claiming ownership is, in this case, meaningless.
2. Whether or not the recipes you created while in their employ fell under the work for hire concept. If they did, then they own them whether copyrightable or not. In the absence of specific contract provisions to the contrary, I suspect that if this got to a court the judge would rule that work for hire does apply. Case law tends to support that view. |