Preparation

1. Oil or spray a 23 by 33 cm (9 by 13 inch) baking pan, and line with parchment paper, allowing the ends of the paper to extend by several inches over the ends of the pan. Set aside.

2. In a mixing bowl, combine the flour, baking powder, cinnamon and sugar. Using a pastry blender or two knives, cut in butter and margarine until the mixture resembles coarse crumbs. Using a fork, mix in the egg until well blended. Shape into a ball, and cover dough with plastic wrap. Refrigerate for 30 minutes.

3. Preheat oven to 177°C (350°F). Using the plastic wrap as an aid in handling the dough, press dough evenly into the bottom of the prepared pan. Bake until evenly golden across the center (the edges may be a bit darker), about 20 minutes. Remove pan from oven and allow to cool on a rack for 10 minutes. Run a knife along the long edges of the pan to loosen the cake. Using the paper extending from the ends of the pan, carefully lift the cake onto a rack to cool.

4. Place a cutting board over the cake on the rack, and invert so that the rack is on top. Remove the rack and paper. Using a sharp knife, cut the cake in half to make two squares. Spread one half evenly with jam. Carefully invert the other half on top, sandwiching the jam between the two layers and trim edges neatly.

5. In a medium bowl, whisk together the confectioners’ sugar and lemon juice to make a thin, smooth icing. Spread evenly across the top of the cake, right to the edges. Allow to sit until completely dry, about 1 hour. Cover loosely with plastic wrap and set aside at room temperature. May be refrigerated; bring to room temperature to serve.

6. Using a sharp knife, cut into bars, squares or diamonds. Arrange on a serving platter.