This chiffon-style pecan cake is rich but also fluffy so it suits a French-style buttercream, which is made using egg yolks, giving it a rich, custard-like taste. Orange is the accent flavour in both the cake and the frosting.
French Buttercream and Assembly
Preheat the oven to 325°F. Grease a dust an angel food cake pan with flour, tapping out any excess flour.
Pulse the pecans with the flour, baking powder & salt until finely ground. Set aside. In a large mixing bowl or in the bowl of a stand mixer fitted with the whip attachment, whip the 5 egg whites until they hold a soft peak when the beaters are lifted. Set aside.
Whip the egg yolks with the sugar, oil, orange juice (or water), orange zest and vanilla for about 3 minutes on high speed until well-blended – the batter will be thick & pale but won’t hold a ribbon when the beaters are lifted. Fold the pecan mixture into the yolks in 2 additions (the batter will be thick at this point). Fold the whites into the batter in 2 additions and pour this in the prepared pan (it will only fill a third of the pan). Bake the cake for about 50 minutes, until it springs back when gently pressed. Cool the cake upside down, in its pan.
For the frosting, place the egg yolks in a large bowl and whip with ¼ cup of the sugar until they are pale and double in volume, about 3 minutes.
Bring the remaining ¼ cup of sugar, the water and lemon juice to a boil over high heat and cook uncovered and without stirring but occasionally brushing down the sides of the pot with water, until it reaches a temperature of 238 °F (softball stage). Carefully pour the hot sugar down the side of the bowl with the yolks while beating on slow speed. Once all the sugar has been added, increase the speed to high and beat until cool, about 6 minutes. Beat in the melted chocolate, then add the butter a few pieces at a time while beating in. Beat in the orange liqueur or brandy (if using), the vanilla and the salt.
Use the buttercream at room temperature. It can be prepared ahead of time and refrigerated, then pulled out to warm up to room temperature and beat until smooth and spreadable.
To assemble the cake, spread the buttercream evenly all over the cake, starting with the top, then the sides and finishing with the hole in the centre of the cake. Arrange the toasted pecans around the top of the cake and chill until ready to serve.