Cut away the skin from the pineapple and cut the flesh into 1 cm (½ inch) slices. Chop into small pieces, discarding the core. Mix together the pineapple and chopped ginger, then scatter in a greased and baselined 20 cm (8 inch) round cake tin at least 4.5 cm (1¾ inches) deep (see
Mix together the polenta, baking powder and ground almonds in a bowl. Beat together the butter, sugar and lime rind in a bowl until pale and creamy. Gradually beat in the eggs. Add the dry ingredients and mix well.
Spoon the mixture into the tin and level the surface. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for about 35 minutes or until risen, just firm to the touch and a skewer inserted into the centre comes out clean.
Meanwhile, make the syrup. Put the sugar and measurement water in a small saucepan and heat gently until the sugar dissolves. Bring to the boil and boil for about 3 minutes or until thickened. Remove from the heat and stir in the lime juice and ginger syrup.
Loosen the edge of the cake and invert on to a serving plate, peeling off the lining paper. Spoon the syrup over the top and serve warm or cold.