In a bowl, whisk together flour, baking powder, chai masala and powdered cardamom. In a small bowl put the saffron strands and the warm milk, mix together and keep aside for the colour and flavour to develop.
In another larger bowl, beat together sugar, butter and lemon zest with a handheld mixer on medium speed, until pale and fluffy (about 2 minutes). Add the eggs and beat well. Now add the saffron-milk mixture and mix until combined. Add the whisked ingredients and beat on slow speed until just combined. Mix in chocolate chips and transfer dough to a work surface.
Divide the dough into two halves and shape each into a log about 11u201d by 1u201d and place on a parchment lined baking sheet leaving some space between them. Refrigerate for about 30 minutes.
Bake at 170C (325F) for about 25 to 30 minutes till the logs look dry and start browning at the edges. Take the baking sheet out of the oven and place on a wire rack. Let the logs cool for 15 minutes.
Place each log on a cutting board and cut into 1u201d thick slices with a serrated knife. Place the slices on the baking sheet, with the cut sides facing up and bake the biscotti for about 15 minutes or so, until they are a light brown in colour. Remove and cool completely on a wire rack. Serve or store in an airtight container.