Gem Cakes in Australia are small, round sweet cakes, usually unflavoured. They are also called Gem Scones, which is perhaps more accurate, as they are more like small scones. You’re meant to serve them with butter, jam, etc.
They are quick to make: from opening the recipe book to baking to the table, the whole process takes about 30 minutes.
There are special pans for making these, made from cast iron or an alloy. The pans consist of, classically, 12 round hemispherical metal moulds, joined together. Some people use Dutch Poffertjes pans, which make 15 at a time. An Aebleskiver pan could also be used. 
Ideally when the cakes bake, the tops of them rise rounded to form a perfect ball.
Compare with New Zealand-style Gem Cakes.
 In America, Australian-style pans were made by companies such as Wagner or Griswold, and called “golf ball pans”
Australian Gem Cakes Recipe (makes 12)
1 tablespoon sugar
1 tablespoon butter
1 egg (beaten)
1 cup milk
2 cups flour
2 heaping teaspoons baking powder
Start oven heating to 425 F / 215 C. Put the gem pan in the oven right away so that it heats, too.
In a large mixing bowl, cream the butter and sugar together, then stir in the beaten egg, then stir in the milk. Put the flour and baking powder into a flour sifter, and sift into the milk mixture. Stir to mix all ingredients.
Take gem pan out of oven. Put a dab of butter in each mould, brush it around in each with a brush. Divide the batter amongst the 12 moulds, and pop back in oven to bake for about 12 minutes.
Take pan out of oven; let stand for 5 minutes, then turn out onto wire rack.