Preheat oven to 425 degrees F (220 degrees C) and place oven rack in the middle of the oven.   Grease, or spray with Pam, a 10 inch (25 cm) x 14 inch (35 cm) pan, line with parchment, and then grease and flour the parchment paper (or spray with Baker's Joy).  Set aside.

In your electric mixer, fitted with the paddle attachment, beat the eggs and sugar on high speed for five minutes, or until pale, thick and fluffy.  (When you slowly raise the beaters the batter will fall back into the bowl in slow ribbons.) At this point beat in the vanilla extract.

Sift half the flour over the egg mixture and fold in gently with a rubber spatula, just until the flour is incorporated.  Sift the remaining flour over the batter and fold in.  Pour the batter into the prepared pan,  evenly spreading the cake batter with an offset spatula.

Bake for 10 minutes or until golden brown.   A toothpick inserted in the center will come out clean and the cake, when lightly pressed, will spring back.

Immediately upon removing the cake from the oven invert the sponge cake onto a clean dish towel that has been sprinkled with confectioners' sugar.  Carefully remove the parchment paper, sprinkle the cake lightly with powdered sugar, and roll up the sponge, with the towel, while it is still hot and pliable. Place on a wire rack to cool.  (If the parchment paper sticks to the cake, lightly brush the back of the paper with a little warm water, allow to stand for a few moments, then peel the paper from the cake.)   

Lemon Curd Filling:

Whip the 1/2 cup (120 ml) heavy whipping cream until soft peaks form.  Add the sugar and whip until stiff peaks form.  Fold the cream into the 1 cup (240 ml) lemon curd.

Assemble:  When ready to fill, unroll the sponge, spread with the lemon curd filling and mashed blackberries, and reroll.  Transfer to a serving platter, cover, and chill in the refrigerator for a few hours.  Just before serving, dust with confectioners' sugar.  Cut the cake into slices using a serrated knife.

Serves 6 - 8