Place the cubed butter and golden syrup into a saucepan stirring till melted
Add the tin of condensed milk and stir on medium heat for approximately 5-8 minutes until the mixture bubbles, thickens and starts to change colour.
Remove from the heat and cool for a couple of minutes before pouring into the chilled crumb crust.
Refrigerate until cold and firm. The pie can be made up to this point and finished when you are ready.