Preheat the oven to 400°F Using a pastry brush, coat the bottom and sides of an ll-by-17-inch jelly-roll pan with 1 tablespoon of softened butter. Line the pan with a 22-inch-long strip of wax paper, and let the paper extend over the ends of the pan.
Brush the remaining butter over the paper, and sprinkle 2 tablespoons of all-purpose flour over it, tipping the pan to spread the flour evenly. Invert the pan and rap it sharply to remove the excess.
With a whisk or a rotary or electric beater, beat the 6 tablespoons of sugar and the eggs together until the mixture is light and fluffy. A little at a time, sift the self-rising flour over the eggs, folding the mixture together gently but thoroughly with a rubber spatula. Do not overmix.
Pour the batter into the jelly-roll pan and, with a spatula, spread it out evenly. Bake in the middle of the oven for 10 minutes, or until the top is a light golden color and the cake has begun to come away from the sides of the pan.
Remove the cake from the oven and dust it evenly with the superfine sugar. Then turn it out on a sheet of wax paper and gently peel off the paper.
Spread the top of the cake evenly with lemon curd and, starting at the long edge, roll it into a cylinder. Cool to room temperature. To serve, cut the cake into 1-inch slices and arrange the slices attractively on a plate.