In a small bowl, beat together the sugar and butter until smooth and creamy. Add the eggs and beat well.
In another bowl, mix together the flours and baking powder. Gradually add to the sugar mixture until all is creamy white.
Gently fold in the ground almonds.
Spoon mixture into greased and floured muffin tin, holding 12. Top each with a sliced almond and bake in a preheated 350-degree oven for about 15 minutes until risen, golden, and firm to the touch. Cool on a wire rack.
NOTE: You can make your own caster sugar if you can't find it in stores. Simply pulse granulated sugar in the blender or food processor until it becomes super-fine (not powdery).