Pour the cold milk into your blender first, followed by 1 cup of the vanilla soft serve ice cream and the vanilla extract. This creates the white base of your shake.
Add 2 tablespoons of chocolate syrup to the blender. Blend on medium speed for 15-20 seconds until smooth and creamy, being careful not to over-blend as this can make the shake too thin.
Pour the blended shake into a tall glass, filling it about three-quarters full. This will be your vanilla-chocolate base layer.
In a separate small bowl, mix the remaining 0.5 cup of vanilla soft serve with 1 tablespoon of chocolate syrup and the heavy cream until you create a thick, swirled chocolate-vanilla mixture.
Gently spoon the chocolate-vanilla mixture on top of the shake in the glass, creating the distinctive black and white two-tone appearance. Swirl slightly with a spoon for visual effect.
Top with a generous dollop of whipped cream and drizzle with chocolate syrup. Serve immediately with a wide straw and long spoon.