Method...well, it wasn't the classic mousse that requires beating yolks and
sugar over hot water and all that. It tooks about 5 minutes to make. It was
more along the lines of a whipped ganache where the chocolate stabilized the
cream, but it is quite dense.

I melted a few oz of Trader Joe's unsweetened baking chocolate in the
microwave, adding heavy cream in several additions as it started to melt and
stirring well. I added enough cream so that it was smooth and liquid and
just warm, not hot. I then poured some more heavy cream into a small metal
bowl, threw in a couple tablespoons of xylitol, and added the chocolate
cream mixture. I tasted it to see if it seemed to be sweet enough, then beat
it with a hand mixer until it started to thicken, and added about 2
tablespoons of very soft butter/smart balance mix because that's what was
out and soft. (Butter helps a mousse set up and gives it good mouth feel.) I
then set it in the freezer for a few minutes to set more quickly.

I just had another spoonful. It's still good today. Sorry not to be more
precise about measurements, but I work with cream and chocolate all the
time, so I was going by appearance and feel.