Preheat oven to 350°F.
Grease two 8-by-2-inch round cake pans.
For the cake: Sift the flour, baking powder, baking soda and salt together into a bowl and set aside.
Cream the butter and sugar in a large bowl with an electric mixer at medium speed until light and fluffy, about 5 minutes.
Reduce the speed to medium-low.
Add the eggs, one at a time, beating 30 seconds between additions.
Add alternating increments of the flour mixture and buttermilk and vanilla, blending well after each addition; this should take about 3 to 5 minutes.
Divide the batter evenly between the prepared pans.
Bake for about 30 minutes, until a cake tester comes out clean.
Cool in pans, on wire racks, for 10 minutes, unmold the cakes and let cool completely.
Note: The cake recipe makes two 8-inch round cake layers.
Only one is used for this recipe.
To assemble cake: Cut the cake in half horizontally.
Place one layer on a cake plate, spread cake with cold custard cream and sprinkle with brittle crumbs.
Cover with the remaining layer of cake.
Spread the remaining custard cream over cake, applying a thinner coat to the sides than the top.
Chill for a least 1 hour before garnishing.
To garnish, press brittle crumbs onto the sides of the cake with the palm of your hand and sprinkle a layer of crumbs on the top.
Refrigerate until ready to use.
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