1. Sieve the flour and baking powder together in a bowl. Whisk the butter and sugar together for 6-7 minutes until pale and creamy. Add the egg yolks, one by one and keep whisking. Then add the grated zest, mastic, rosewater, lemon juice and flour. Finally add the almonds and the egg whites whisked to a meringue. Fold them gently in the mixture with the help of a spoon until fully incorporated.
2. Grease with butter and line with greaseproof paper a 30cm baking tin. Empty the mixture in.
3. Bake the cake at 170ºC, for 50 minutes until it rises and comes easily off the sides of the tin.