Combine the chocolate with heavy whipping cream in your microwave safe dish. Heat in microwave for 30-second intervals. In between intervals, remove the dish and whisk/stir the mixture together.
You may need to add more chocolate to make it thicker or more cream to thin it out.
Let it cool for a few minutes before pouring it in the bottle.
Once at the perfect temperature, use the bottle to place the ganache on the edge of the top of the cake. It will drip down the cake creating that cake drip effect. If it runs down the side of your cake the ganache needs to cool a little longer or you can add more chocolate to it to cool it down faster and make it thicker.