Preheat the oven to 170°C (325°F), and butter and flour a 19 x 19 x 8 cm (7½ x 7½ x 3¼ in) loaf tin. Weigh the eggs, then weigh out the same amount of butter, sugar and flour. Using an electric mixer, beat the sugar and butter together for 5 minutes, or until light and creamy. Add the