Transubstantiation is, according to the teaching of the Catholic Church, “the change of the whole substance of bread into the substance of the Body of Christ and of the whole substance of wine into the substance of the Blood of Christ.– Wikipedia
As far as I remember, Douglas Harding (Headless Way), mentioned transubstantiation. I hold bread or a glass of wine, I move it into my mouth, and it disappears. It becomes what I am, which is awake capacity for it all. It becomes Spirit.
It’s perhaps more accurate to say it never was not Spirit. To me, the bread and wine always is what I am, it’s awake capacity temporarily taking the form of bread and wine. It happens within and as what I am.
So the real transubstantiation happens within us. It’s the shift from taking bread and wine as only bread and wine, to recognize we are capacity for it, and they happen within and as what we are.
There is ultimately no real transubstantiation since it never was not that. It never did not happen within and as what we are. It never did not happen within and as Spirit.
Bread and wine here stand is for all of existence, they are metaphors for all there is as content of our experience. And Christ here stands for what we are, for our true nature and possibly the true nature of all existence. (There is also a unique quality or characteristic of the Christ energy/consciousness, which we can get to know through Christ-centered practices like the Heart/Christ Prayer and Christ meditation.)