Preheat your oven to 350°F (180°C). Place about 40 petit four cases (mini paper cupcake liners) on a baking sheet.
In a large bowl, mix the softened butter and sugar until smooth. Add the eggs, then stir in the flour, baking powder, salt, and milk. Use a hand mixer or spoon to beat everything until you get a smooth batter.
Use a small spoon to fill each paper case about halfway. Don’t add too much—the cakes rise while baking.
Bake for 15 to 20 minutes or until they turn pale golden and spring back when touched. Remove from the oven and let them cool on a wire rack.
While the cakes cool, make the icing. Put the confectioners’ sugar in a bowl and slowly stir in lemon juice until it’s smooth and thick but spreadable.
Spoon a little icing on top of each cooled gem. Use the back of the spoon to spread it gently. When the icing starts to set, press a small candy or sweet into the center.