To make vasilopita, combine butter, sugar, eggs and citrus rinds, add flour and salt, pour the batter into a pan, hide a coin in the batter, and bake the cake for 45 minutes. This is a traditional Greek recipe served on New Year's Day.
Grease a 10-inch springform pan, and preheat the oven to 350 F. Use a zester to grate the rind of 2 oranges and 2 lemons into a small bowl.
Place 2 sticks unsalted butter in the bowl of an electric mixer, beat it on high speed until it is light and fluffy, and then mix in 1 cup white sugar. Crack a large egg into the bowl, and whip it into the sugared butter. Repeat with two more eggs. Add the citrus zest, 1/2 teaspoon powdered sour cherry pits and 2 teaspoons powdered gum mastic. Whip the mixture to incorporate these ingredients.
In a separate bowl, combine 4 cups white flour, 2 teaspoons baking powder and 1/2 teaspoon salt. Sift the dry ingredients together.
Pour 1/2 cup milk into a measuring cup, and turn on the electric mixer. Add a small amount of the dry ingredients, and then some of the milk. Continue adding the milk and dry ingredients until you have a uniform batter.
Pour the batter into the springform pan. Wrap a clean coin in foil, and hide it in the batter. Smooth the top of the batter to camouflage the location of the coin. Whisk 1 egg yolk with 1 tablespoon milk, brush the glaze over the batter, and sprinkle the cake with sesame seeds. Press blanched almonds into the top of the batter in a cross shape, and use the remaining nuts to form the number of the new year.
Bake the cake for 45 minutes, let it cool for 15 minutes, and then release the sides of the pan.