180°C, 350°F, Gas Mark 4
Serves 12

Ingredients

Sift flour, ¾ cup sugar and the salt onto a sheel of wax paper; set aside. Using an electric mixer, beat egg yolks with ¼ cup sugar until thick and pale yellow. Add water and beat until thickened, about 4 minutes. Whisk egg whites in bowl of a heavy-duty mixer until just frothy. Add cream of tartar; whisk until soft peaks form. Add remaining ½ cup sugar in a steady stream, whisking until thicker, stiffer, glossy peaks form - about 2 to 3 minutes. Whisk in vanilla, lemon juice and lemon zest. Pour yolk mixture over whites. Fold together with rubber spatula.

Using a metal spatula, scoop up a third of the flour mixture and sprinkle over mixture; fold in with a rubber spatula. Repeat two more times until ingredients are just incorporated. Gently pour batter into an ungreased 10-inch round tube pan with removable bottom. Level top with a rubber spatula. Bake for 50 to 55 minutes, or until top springs back slightly when lightly touched. Allow to cool for about 45 mins and then remove from pan. Cover cake with a rack, and invert; remove bottom of pan.

Coffee Crunch Topping:
Generously oil a large baking sheet; sift baking soda onto a sheet of wax paper; set nearby. Combine coffee, sugar and corn syrup in a heavy, 4-quart saucepan. Place over medium-low heat, stirring occasionally, until sugar dissolves. When mixture is clear and begins to boil, increase heat to medium-high; cook until mixture reaches 290°F on a candy thermometer.

Towards the end of the cooking (around 270-280°F), stir occasionally to prevent mixture from scorching and becoming too foamy. Remove from heat and stir in baking soda (mixture will foam up fiercely). While still foaming, pour out onto oiled baking sheet. Do not spread; let cool, undisturbed for at least 1 hour. Crush into very small pieces. (Place between 2 sheets of wax paper and tap or roll with rolling pin.) Store in an airtight container.

For the frosting: Combine cream, sugar and vanilla; beat until cream holds soft peaks.

To assemble: Slice cooled cake into three equal layers using a serrated knife. Spread whipped cream between each layer, carefully stacking layers. Spread remaining whipped cream over top and sides of cake. Refrigerate. Just before serving, generously sprinkle top and sides with the coffee crunch.