Mix water and arrowroot powder then set aside
In a small sauce pan on medium heat, melt butter
After butter is melted pour in heavy cream
As it's heating up which it will very fast slowly pour in arrowroot/water mix a little at a time while still mixing. The cream will thicken quickly so don't burn it.
Remove from heat and add in cheese then continue stirring (see notes below)
Cycle putting it on the heat source then taking it back off until cheese is fully melted.