Preheat the oven to 350F
Grease a 10" cake or springform pan. Lining with parchment paper also works.
Cream the sugar and butter until light and floofy.
Stir in the flour, and mix until the mixture is fairly smooth.
Mix in the eggs, one at a time (see #2 below).
Stir the baking powder into the milk, add to the batter, and mix well.
Mix the baking soda and citrus juice, and quickly stir into the batter.
Pour the batter into the prepared pan.
Bake for 20 minutes, add the coin ( see #3 ), and return to the oven for another 20-30 minutes. Toothpick test after a total of 40, and test every 3 minutes after that.
Remove from pan, and let cool on a rack for 10 minutes before dusting/glazing (see #4) and serving.