Should I have been able to melt white chocolate and marshmallows together?
This is definitely possible, though I should add that the addition of melted butter would be crucial.
Do not simply toss &quot;raw&quot; marshmallows into the melted white chocolate, as they will start to cool down the chocolate more than you'd think (I once tucked my hand into a bag of marshmallows, it was relatively cold in temperature).
Here is how I would do it:

Melt some butter in a pan (don't skimp!).

Toss in your marshmallows and constantly stir them, until all melted and silky.

Pour the melted white chocolate into the melted marshmallow &amp; butter, and continue to heat and stir for a few minutes.