Marque number XXVI (26) in the Exceptional Cask Series is the curiously named 'Magisterium', a blend of three 16-year-old single blended rums distilled in two stills: a Double-Retort Pot Still and a Continuous Twin Column Coffey Still. Out of the three rums, two were double-matured. One spent three years aging in ex-bourbon casks and 13 years in ex-oloroso sherry barrels; another spent nine years in ex-bourbon casks and seven years in ex-oloroso sherry. The third component was matured exclusively in ex-bourbon barrels for 16 years. That makes it the first heavily sherried expression since the ECS Sovereignty, widely regarded as a series favourite. The make up should appeal equally to lovers of dark, brooding cask strength single malts, as much as Foursquare fans. The final rum is bottled at 58% Alc./Vol.