Preheat your oven to 350°F (175°C). Grease a round cake pan.
In a large bowl, cream the butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Sift together the flour and baking powder, then add to the batter alternately with the milk, beginning and ending with the flour mixture.
Stir in the vanilla extract.
Pour the batter into the prepared cake pan. Insert the wrapped coin into the batter.
Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center comes out clean.
Let cool for 10 minutes in the pan before transferring to a wire rack to cool completely.