For the mini sand cakes, cream the butter with the sugar until very fluffy. add the eggs salt and rum and continue to stir. Mix the flour and cornstarch with the baking powder, sift into the butter-sugar mixture and stir in as well.
The dough should have a fine very creamy consistency. If it is too firm, add a little milk. Pour the dough into small baking cups (made of selicone or greased) and bake the cakes in the oven at 170 °C for about 30 minutes. Test with chopsticks.
Turn out the finished cakes and let them cool on a cooling rack. If necessary, sprinkle with a little powdered sugar.