In a bowl, using a hand held mixer, cream the butter and sugar till soft and fluffy. Add the egg and the vanilla extract and beat well.
Sift together the flour, baking powder and salt and add to the bowl and mix well to form a softish dough.
Melt the semi-sweet chocolate over warm water and allow it to cool.
Take 2/3rd of the dough out of the bowl and keep it aside. Add the baking soda to the melted chocolate, stir well and add it to the 1/3rd portion dough which is in the bowl. Knead this well so that you have a brown coloured dough with no streaks visible.
Chill both doughs for about 1/2 an hour to make the dough easy to work with.
Take light coloured dough and divide into 2 equal portions. Also similarly divide the chocolate dough into 2 portions and roll each portion into a long cylinder/ rope shape about 10u201d long. Keep aside.
Cut out a piece of aluminum foil (approx. 12u201d by 6u201d). Place one piece of light coloured dough in the centre of the piece of foil and roll it out into 10u201d by 4u201d rectangle. Place one chocolate dough cylinder/ rope in the centre of this rectangle.
Using the foil, wrap the light coloured rectangle of dough around the chocolate one from both sides. Your dough should now look like long roll of light coloured dough with the chocolate dough in the centre. Wrap the aluminium foil aroung the roll.
Repeat this with the other half of both doughs, and chill both rolls of dough for at least 2 hours or even overnight.
When ready to bake the cookies, remove the foil and slice each roll of dough into 1/4u201d thick slices and place them on lined baking sheets.
For each owl, press two slices together to form a face.
Pinch, or shape the outer corners of each slice to form u201cearsu201d and push an upside down chocolate chip in to the centre of each slice to make u201ceyesu201d.
Press a whole cashewnut between the slices, with pointed side down to make a u201cbeaku201d.
Repeat with all the slices.
Do leave some space on the cookie sheets between u201cowlsu201d as the will swell up and become larger as they bake. Bake the owl cookies at 108C (350F) for about 10 to 15 minutes till the edges of the cookies start becoming brown.
Cool the cookies on the sheets for about 5 minutes and then carefully remove them racks to cool completely