Preheat the oven to 325 degrees F.
Butter the sides of an 8-inch springform pan
, and line the base with greaseproof or parchment paper.
In a large bowl or in an electric food mixer
, cream the butter until soft. Add the sugar, and beat until the mixture is light and fluffy. Gradually add the beaten eggs
, beating well between each addition.
in the flour and baking powder, add the poppy seeds, and stir until combined.
Spoon the mixture into the prepared cake pan
, making a slight hollow in the center with the back of a spoon. Bake in the oven until the cake is cooked in the center and a skewer
inserted into the middle comes out clean, about 25 to 28 minutes.
Allow the cake to stand for 5 minutes before carefully removing it from the pan and transferring it to a wire rack to cool completely.
If you wish, when the cake is cool, split it in half using a long-bladed serrated knife. Place one layer of the cake on a serving plate and spread over 2 generous tablespoons of the vanilla buttercream, then place the other half of the cake on top. Spread the remaining icing over the top and sides with a palette knife or table knife. The cake can also be kept whole, with the icing spread over the top and sides.