Cake: use your favorite white sponge cake recipe, bake and let cool.

Crunch: 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 degrees on a candy thermometer. Toward the end of cooking (270 to 280 degrees), stir occasionally to prevent mixture from scorching and becoming too foamy).

Crunch: 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 with a utensil, but tilt the baking sheet to coat the bottom; let cool undisturbed for at least 1 hour.

Crush into very small pieces. (Place between 2 sheets of parchment paper and tap or roll with rolling pin.) Store in an airtight container.

Frosting: combine cream, sugar and vanilla in a heavy-duty mixer; beat on high speed until cream holds soft peaks.

Assemble: frost the layers with the frosting. Refrigerate the cake. Just before serving, sprinkle the coffee crunch over the top and sides.