Place butter, glucose syrup, and sugar in a medium saucepan over a low heat. Cook, stirring, until butter is melted. Add the condensed milk and cook, stirring, for 3-5 minutes or until the sugar dissolves and mixture is smooth. Increase heat to medium-high. Cook, stirring constantly, for 10-15 minutes or until mixture is thick and becomes caramel in colour. Remove from the heat.