In bowl, mix together sugar, cornstarch, flour and salt; whisk in egg and remaining 1/2 cup cold milk.
Gradually whisk in hot milk and return to saucepan.
Cook over medium heat until mixture thickens, then remove from heat and stir in margarine and vanilla extract then refrigerate.
Line bottom of 13 x 9 inch baking pan with wax paper. Lightly coat paper with cooking spray.bowl, In a bowl beat eggs and sugar until thick. Gradually beat in water, vanilla extract and almond extract.
In another bowl, sift together flour, baking powder and salt. Gradually add to egg mixture, mixing until just blended. Pour evenly into prepared pan. Bake for 12 minutes, or until center of cake is springy to touch. Cool 5 minutes.
Dust tea towel with icing sugar and turn cake out onto towel. Carefully peel off paper. Roll up cake and towel together, lengthwise; cool completely.
To assemble trifle: Unroll cake and spread with jam; roll up again and cut into 1/2 inch slices and arrange in serving bowl. Top cake slices with fruit and custard. Cover and refrigerate 4 hours or overnight.