Pre-heat the oven to 180C/350F/Gas 4.
Sift the icing sugar, flour and cornflour together into a bowl. Add the ground almonds.
Cut the butter into cubes and add it to the dry ingredients. Using your fingers, a mixer or food processor, rub or mix the butter in until there are no visible lumps of butter. Add the almond essence.
Turn the mixture out onto a lightly floured surface and knead a few times, just to form a smooth dough.
Butter a muffin tin. Roll the dough into small balls and place them in the muffin cups, flattening the tops slightly with your fingers. The dough should come about one-third of the way up the side of the pan. 6. Bake the shortbreads until they are a light gold colour, about 8-12 minutes. Remove them from the oven and, using your selected tool, make a small indentation in the top of each biscuit.
Let the shortbreads cool for a few minutes, then turn the mould over and tap it over the bench so that the shortbreads fall out. Be gentle, as they are fragile while they are still warm.
When all the shortbreads are baked and cooled, dust the tops with some icing sugar. Using a teaspoon, fill the indentation with jam or your chosen filling.