Preheat oven to 180 degrees C. Generously grease a 25cm round cake tin.
In a medium bowl, cream the butter and sugar together until light. Stir in the flour and mix until combined-it may be a little dry and crumbly. Add the eggs one at a time, mixing well after each addition. Combine the baking powder and milk, add to the egg mixture, mix well. Then combine the lemon juice and baking soda, stir into the batter. Pour into the prepared cake tin.
Bake for 20 minutes in the preheated oven. Remove and sprinkle the nuts and sugar over the cake, then return it to the oven for 20 to 30 additional minutes, until cake springs back to the touch. Gently cut a small slit in the cake with a knife and place a coin in it. Try to cover the slit up.Cool cake on a rack for 10 minutes before inverting onto a plate.