How does Life Transference work with Supreme Healing from Life Domain?

Question

So the Life Transference spell in 5e does the following:

You take 4d8 necrotic damage, and one creature you choose and can see regains hit points equal to twice the damage you take.

I have a cleric in my group that has taken the life domain and soon will reach level 17, where they get the Supreme Healing ability:

Starting at 17th level, when you would normally roll one or more dice to restore hit points with a spell, you instead use the highest number possible for each die. For example, instead of restoring 2d6 hit points to a creature, you restore 12.

So how does this work with the spell Life Transference? The spell does healing, but not directly as it first has to siphon off health from the cleric, as the dice rolled are not for healing but for necrotic damage. Is the damage always maximized resulting in maximized healing?

Answer 1

This has been answered in this Sage Advice from Jeremy Crawford.

Disciple of Life works with life transference. Supreme Healing does not.

Unfortunately the Life Domain's Supreme Healing feature does not interact with the Life Transference spell.

Also, in addition to this:

Life transference restores hit points. Blessed Healer keys off restoring hit points. They work together.

Answer 2

"..when you would normally roll one or more dice to restore hit points.."

Using Life Transference you do not roll any dice to restore hit points. You are rolling for necrotic damage. If you found a way to maximize necrotic damage, you could do 32 necrotic damage to yourself and heal your target for 64.