1.Position oven shelves; preheat oven to 160°C. Grease deep 20cm-round cake pan; line base with baking paper.
2.Blend or process nuts until finely ground.
3.Beat butter, rind, sugar and egg in small bowl with electric mixer until light and fluffy. Transfer mixture to large bowl; using wooden spoon, stir in brandy, nuts and flours. Spread mixture into prepared pan. Bake about 1 hour.
4.Meanwhile, to make lemon syrup, combine ingredients in small saucepan. Using wooden spoon, stir over heat, without boiling, until sugar dissolves; bring to a boil, remove from heat.
5.Pour hot lemon syrup over hot cake in pan. Cover pan tightly with foil; cool cake to room temperature. Cake with syrup can be kept in an airtight container for up to 2 days. Cake without syrup can be kept in an airtight container for up to 2 days, and can be frozen for up to 3 months.
The walnuts, ground very finely, make up the majority of the “flour” content of this mixture. Any kind of nut can be substituted for the walnuts. Buy exactly the same weight of either ready-ground nut meal or of nut pieces that you blend or process yourself. Pecans and orange, instead of lemon, is another good combination. Rum is a good substitute for the brandy, or you can use fruit juice if you don’t want to use alcohol.