This cake is as pretty as a picture. The combination of flavours really works – the citrus of the lemon bringing out the zesty notes in the basil.
Heat the oven to 180°C/160°C fan/350°F/Gas 4.
Make the sponge. Beat together the butter and sugar in a stand mixer fitted with the beater, on medium speed until pale and fluffy. Beat in the eggs, little by little, until well combined. Then, using a metal spoon, stir in the flour and baking powder. Lightly beat in the chopped basil and remaining cake ingredients (except the rose petals), mixing until smooth. Spoon the mixture into the bundt tin and bake for 55–60 minutes, until a skewer inserted into the sponge comes out clean. Leave to cool in the tin for 15 minutes, then turn out onto a wire rack to cool completely.
Make the glaze. Place the sugar, limoncello and lemon juice in a very small pan and cook over a low heat until the sugar has dissolved. Then, increase the heat and boil for 2–3 minutes, until reduced to a slightly syrupy consistency. Brush the syrup all over the cooled cake.
To make the basil sugar, place the sugar and the basil leaves in a mini chopper or mortar and blend, or pound with the pestle, until the sugar has turned green. Sprinkle this between the ribs of the cake.
Make the buttermilk icing. Mix the icing sugar with the buttermilk, lemon extract and lemon juice to a thick, piping consistency. Drizzle the mixture over the cake using a teaspoon. Sprinkle with rose petals to finish.