Chop up the chocolate finely and place it in a heat proof bowl.
Heat the cream in a saucepan over medium until it's steaming but NOT boiling.
Pour the steaming cream over the chocolate. Cover the bowl to keep the warmth in. Let it sit for a few minutes for the chocolate to melt. Then, stir it all together until it's smoothly blended.
Use a good-quality baking chocolate here, rather than chocolate chips.
Chop the chocolate as finely as possible, so it will melt completely and evenly.
Use heavy whipping cream, not half and half or anything lighter.
Chocolate ganache will thicken as it cools. If you want to drizzle it over a cake so that it runs down the sides, use it right away while it's still warm. If you want to spread it out thicker over a cake layer, allow it to cool more.
Leftovers will keep in the refrigerator for a few days. Gently reheat it, stirring frequently, to use it again.