Gather all your ingredients and tools. Make sure you have everything ready to go.
In your blender, combine the milk, ice cream, chocolate cake mix, 2 tablespoons of chocolate syrup, and vanilla extract.
Blend the mixture on high until it becomes smooth and creamy. Adjust thickness by adding more ice cream or milk as needed.
Taste your milkshake and adjust sweetness by adding more chocolate syrup if desired.
Pour the milkshake into serving glasses and top with whipped topping and sprinkles if desired.