Add milk, whisky, malted milk powder, chocolate ice cream, and ice to the blender. Add 2 to 4 ounces of whisky (a 2-ounce addition of whiskey will give a more subtle taste of alcohol, while 4-ounces will be a much stronger flavor).
Blend on low, slowly increasing the speed until smooth consistently is reached, about 2 to 3 minutes. Add more milk if a thinner milkshake is desired.
In a large chilled bowl, whisk chilled whipping cream, sugar, and vanilla until soft peaks form.
Pour chocolate malted whisky milkshake into 4 separate glasses (8 ounces per glass). Top with fresh whipped cream and garnish. Cheers!