Preheat oven to 350 f
Cream butter and sugar
Add egg yolks and mix
Add Dark Rum and mix
Combine flour and salt
Add to wet mixture gradually while mixing
Knead with dough hook for 4 minutes
Grease an 8 inch spring form pan
Press dough into place evenly and smooth top with a spoon
Score top with a fork in the classic pattern
Combine egg yolk and water to make an egg wash
Brush the top of the dough with the egg wash
Bake in a middle rack for 40 minutes