Bring 1 ½ Cups of heavy cream to a boil.
In a deep bowl or measuring cup, pour the boiling cream over 3 ¼ Cups or an 18 oz bag of semi-sweet chocolate chips.
Whisk until all the chocolate chips are melted and the mixture is completely smooth.
Allow to cool until the ganache is still pourable but not a hot liquid.
Loosen the mousse cake by running a sharp knife around the edges.
Remove the springform pan rim.
Once the ganache has cooled to a pourable but not hot state, pour some over the top mousse cake, spreading it carefully, allowing it to run down the edges and smoothing it around the edges as well.
You will use ⅔rds of the ganache to coat the cake.
Press mini semi-sweet chocolate chips to the ganache-coated sides of the cake. Yes, this is a bit messy.
Place the cake back in the fridge and let it chill while the remaining ganache cools and sets up to a pipeable consistency.
If you want to transfer the mousse cake to a cake plate, this is time.
Carefully slide a spatula under the mousse cake and loosen the entire cake from the springform pan bottom.
Carefully slide onto a cake plate.
Scoop the ganache into a frosting bag fitted with a large decorative tip of your choice. I usually use a large star tip.
Pipe the ganache around the top and bottom edges of the mousse cake.
Melt the white chocolate and drizzle or pipe over the middle of the cake.
Place the cake back in the fridge to set the ganache and chill all the way through for at least 4 hours.
Slice and serve when ready.