Preheat oven to 170g degrees C. Grease and flour a 25cm ring tin. Mix together the flour and baking powder.
In a large bowl cream together 250g butter, 125g copha and 2 cups sugar until light and fluffy. Beat in the eggs one at a time. Beat in the flour mixture alternately with the milk mixing just until incorporated. Stir in 2 tablespoons rum, lime zest, 2 teaspoons lime juice, vanilla essence and lemon juice.
Pour batter into prepared pan. Bake in the preheated oven for 90 minutes or until a toothpick inserted into the centre of the cake comes out clean. Allow to cool in pan 10 minutes. Turn it out onto wire rack. While warm prick top of cake with toothpick. Pour lime glaze over warm cake. Cool completely.
To make lime glaze: In small saucepan combine 1/4 cup sugar, 65g butter and 2 tablespoons lime juice. Boil, stirring constantly, for 1 minute. Remove from heat and stir in 3 tablespoons rum.