Place the eggs, sugar, milk and vanilla into a medium size jug or mixing bowl.
Use a whisk or fork to mix until well combined and the sugar has dissolved.
Divide the mixture evenly between four ramekins.
Cover each ramekin with foil.
Place the ramekins into the slow cooker.
Carefully pour hot water down the side of the slow cooker. Fill until the water comes halfway up the sides of the ramekins.
Put the lid on the slow cooker, set to low and cook for 2 ½ - 3 ½ hours or until set.You can tell when a baked custard is set because, it will juggle and wobble slightly like set jelly when the dish is shaken. Carefully remove the ramekins from the slow cooker and place on a wire rack, remove the foil cover and allow to cool.
Chill for several hours if you like a cold custard or if you prefer it can be served warm.