Too bad that happened to the chocolate, although I am not sure why it happened. Even if you mix water into chocolate it will not harden the chocolate. After all you can make a hot chocolate out of molten chocolate and water (milk is preferable but water works). You say you mixed a batter in it. Maybe the temperature difference was simply too big. I don't know what was wrong.

For a quick safe, some caramel, simply whipped up in a pan with milk, cream and sugar will work. Or put some mixed berries on top. If the berries don't look so hot anymore, puree them.

Some grated dark chocolate would also look really nice on a white cheesecake.

Besides that, I'm not spoiled. I will even eat plain cheesecake. Now you made me hungry!

Till