Lemon Filling Rolled Cake

Preheat oven to 375°F (190°C).

Lemon Curd
In saucepan over medium-high heat, heat sugar, butter, lemon rind and juice, stirring until sugar dissolves and butter is melted. In bowl, whisk eggs; slowly whisk in lemon mixture. Return to saucepan and cook, stirring constantly, just until boiling; simmer for 1 minute. Pour into bowl. Place plastic wrap directly on surface; chill in refrigerator for about 3 hours or until completely chilled. Whip cream; fold into lemon mixture.

In large bowl, beat egg yolks with 1/2 cup of the sugar for 3 minutes or until pale and thickened; blend in vanilla. In separate bowl and using clean beaters, beat egg whites with cream of tartar until soft peaks form; gradually beat in remaining sugar until stiff peaks form. Combine flour and salt. Fold egg whites into yolk mixture alternately with flour, making 3 additions of egg whites and 2 of flour.

Spread in parchment paper lined 17 inch x 11 inch jelly roll pan. Bake in oven for 12 to 15 minutes or until top springs back when touched. Dust tea towel with icing sugar. With knife, loosen edges of cake; invert onto towel. Carefully remove pan and paper; trim 1/2 inch off edges with serrated knife. Starting at long edge, immediately roll up cake in towel; let cook on rack.

Unroll cake. Spread evenly with lemon mixture. Sprinkle with blueberries, if using. Using towel as support, roll up cake without towel. Place seam side down, on platter. Dust with icing sugar.