In a bowl combine the milk and butter. Heat until the butter melts fully in a small saucepan over medium heat or in the microwave.
Transfer to a blender and blend on the highest speed for 5 minutes. Every 30 seconds, lift the center of the cap to release steam.
Pour the mixture into a small bowl and place a piece of plastic wrap directly on the surface to prevent a skin from forming.
Let it come to room temperature before refrigerating it for at least 4 hours (or overnight).
Stir in the sugar and vanilla extract if using and then pour the mixture into a medium bowl and using a handheld electric mixer, whip on high speed for 3-5 minutes, until desired stiffness is reached.
Use immediately or refrigerate for up to 2 hours. (Unwhipped cream can be stored in the refrigerator for up to 4 days.)
