Add the diced ginger, cornstarch, cocoa powder, and 2 - 3 tablespoons of milk to a small saucepan.
Heat on medium-low and whisk well as the mixture heats up. The milk will begin to thicken, and as it does, add the chocolate, molasses, cinnamon, nutmeg, sugar, and salt.
Stir in about a third of the milk slowly as the chocolate begins to melt. Once the chocolate is fully melted, add in the remaining milk and stir well.
Whisk vigorously for about a minute as the mixture comes to a boil. Turn off the heat.
Place a small fine-mesh strainer over your mug and pour the hot chocolate through the strainer. There may be thicker parts of the hot chocolate that you need to press through. This is normal. Just press it through and stir it back in.
Make the whipped cream by beating the heavy cream, powdered sugar, and a tablespoon of the Torani white chocolate sauce until it forms stiff peaks.
Spoon over your hot chocolate. Drizzle with more white chocolate sauce.