Preheat oven to 175 degrees C (350 degrees F). Grease cookie tins.
In a large bowl, use your hands to mix together the almond paste, flour, egg whites, caster sugar and icing sugar until well blended. The mixture will be very sticky. Place the sliced almonds into a small bowl. Scoop out rounded teaspoonfuls of the dough and drop them into the almonds. Roll until completely coated. Place 3cm apart onto the prepared cookie tins.
Bake for 15 to 20 minutes in the preheated oven, until golden brown. Cool on cookie tins for a few minutes before removing to a wire rack to cool completely.