In a small bowl, melt the chocolate into your microwave oven in 10 seconds increments, stir with a spoon on each pause, dont burn your chocolate, mix in the sifted cocoa powder, set aside to cool.
Beat the butter and sugar on high speed until light and fluffy, about 3 to 4 minutes, beat in the egg and vanilla extract.
In a separate bowl, whisk together the flour, salt and baking powder, add to the butter mixture, beat in on low speed just until all mix. dont overbeat.
Remove half of the dough, add the chocolate mixture to one half of dough and mix with a spatula.
Make cookies.
Bake for 12 to 15 minutes or until done.
Cool at least 10 minutes, dont touch the cookies right out of the oven as they will be very soft.
Marble biscuits are ready to serve.
