1Grease and dust a 6" round tin and keep it aside .Pre heat the oven at 150 degree C. Roast the pistachio and chop it with a knife .
2Keep sweet lime zest ready. In a small bowl beat the egg gently. Keep it aside. Sift the flour and baking powder thrice.
3In a medium sized bowl , cream butter and sugar well using electric mixer.Add sweet lime zest. Add beaten eggs. Gently fold in flour , sweet lime juice and water .Be very careful not to stir the batter. Gently fold in roasted and chopped pistachio .
4Now divide the batter into two parts.
5Mix mix instant coffee powder in 3/4 tbsp of warm water.
6Gently mix it his into one portion of batter.
7Spoon in the batter i into the prepared cake tin.
8Bake at 150 degree C for 35 mins or until done.