Leave the butter in a container at room temperature to soften. Beat the butter and sugar for awhile until you get a fluffy cream. Add the eggs 1 by 1, the baking soda, which has been pre-dissolved in 1 cup of warm water.
Finally, mix this with enough flour to get a soft dough. Spread out 3/4 of the dough in a greased tray. Brush the top with plenty of marmalade - the flavor can be enhanced by adding 2 vanillas, 1 tablespoon rum or cognac.
Spread the remaining butter on top and mix it with more flour until you get a much firmer dough. Grate it on top of the marmalade, gently press down and put the cake to bake in a moderately heated oven.
Serve the butter cake with marmalade sprinkled with powdered sugar.