Dear Rabbi Simon
We have plastic covers used in the microwave to cover the plate. By accident today I put the milky one on a meaty plate full of chicken and microwaved it for a minute or so before I realised. What should we do about the milky cover and collateral damage?
The food and the plate are fine, however I would suggest buying a new cover, as it is questionable if plastic can be kashered, and those plastic plate covers are not expensive. Also, immersing in boiling water may be more than it can take.
I would add, however, that it is not recommended to use a microwave oven for meat and dairy both, but rather to designate it for one or the other. Parve you can use in it either way, as long as it is clean. One advantage of such a policy is the avoidance of errors of the type discussed above.
Rabbi Rashi Simon