Pre-heat oven to 180°C / 160°C (fan-forced). Grease and line a 20cm base diameter cake pan with baking paper.
Add butter, maple syrup, vanilla and soy sauce to the bowl of an electric stand mixer. Whisk for a couple of minutes until pale and creamy. Add eggs one at a time and continue beating until you get a fluffy and creamy mixture.
Add lemon zest, spelt flour, cornflour, baking powder and milk. Beat for a brief few seconds until just combined. Alternatively, fold these ingredients gently into the egg mixture using a wooden or silicone spoon until just combined.
Spoon cake batter into the prepared tin. Bake in the preheated oven for 40 minutes until golden and cooked through the middle.
Remove from the oven and allow to cool in the tin for a bit. Remove carefully onto a cake plate when cool. Dust with icing sugar and serve.
Soy Sauce Substitution - If you don't want to use soy sauce, substitute with a pinch of salt instead.Simple Icing - In her book, Amber tops the cake with a simple icing made by whipping cream and honey together. I have tried this and it is quite lovely too.Sweetness - This isn't a very sweet cake to begin with. If you like your cakes sweeter, just dust with more icing sugar when serving or serve with a dollop of ice cream or sweetened whipped cream with berries.