Preheat the oven to 350°F. Grease and flour a savarin mold.
Beat the butter until it is light and fluffy. Beat in the the sugar and vanilla, creaming well. Add the eggs one at a time and beat well after each.
Mix together the flour, baking soda, baking powder, and salt. Alternate adding this to the batter with the yogurt (three parts dry ingredients, two parts yogurt), beating well after each addition.
Spread the batter evenly in the prepared pan. Bake at 350°F for 45 minutes, or until a cake tester comes out clean.
Cool on a wire rack for a few minutes, then turn out onto another rack to completely cool.
Cream together the powdered sugar, butter, cocoa, and whipping cream until well blended. You may need to add a little more whipping cream to get the icing to good decorating consistency.
Place the cake on a serving dish. Fill a cake decorating bag with the icing and use a plain round tip to create strings all over the cake (think like a bird building her nest). Place the candy eggs in the center.
