While the cake chills, make the white chocolate ganache drip.
Heat the heavy cream in a heat proof bowl in the microwave for 30-45 seconds, until it's steaming and just beginning to bubble.
Gently pour the heavy cream over the white chocolate chips, making sure they are fully covered with cream. Allow the mixture to sit for 1 minute.
Stir slowly until the cream and white chocolate are combined. Some bits of chocolate may not be fully melted yet. If you notice this in your mixture, heat the mixture again for 15 seconds and stir. Repeat as necessary until all the chocolate bits are fully melted and incorporated.
Once the ganache is smooth, mix in the white gel food coloring until the ganache is evenly colored. If you plan to use a plastic bottle to add your drips, pour the mixture into a plastic bottle.
Let the mixture cool until the desired viscosity is reached and it's barely warm to the touch.
If it seems too thin or thick, you can add a touch more chocolate chips or heavy cream! The type of cream and white chocolate that you use can affect the consistency, so feel free to adjust as needed.
Make a test drip with your ganache to see if it's the right consistency, then adjust as needed (i.e. if the ganache is too thin let it cool more or add more white chocolate, or if it’s too thick pop it in the microwave for 5 seconds or add a tiny bit more heavy cream).
Once it's the right consistency, add the drips to the chilled cake using a plastic squirt bottle or spoon. After covering the sides of the cake with drips, chill the cake in the freezer for 5 minutes to help the drips set.
Add some of the remaining ganache on top of the cake and carefully spread it over the top of the chilled cake.
Then decorate as desired! I like to add a fun sprinkle blend around the base of the cake and use the leftover buttercream to pipe dollops on top of the cake using your favorite frosting tip (I used a Wilton 1M).