Preheat the oven to 350 degrees and line a small loaf pan with parchment paper.
Stir the flour and baking powder together in a bowl. Crush the saffron threads lightly and set them aside.
Beat the butter and honey until smooth. Add the eggs one at a time, mixing well after each addition.
Stir in the milk and the saffron. Add the flour mixture and mix just until no dry streaks remain.
Pour the batter into the prepared pan and bake for 30 to 35 minutes, until a toothpick comes out clean. Let the cake cool in the pan for 10 minutes, then move it to a wire rack.
Whisk the powdered sugar with the rosewater until smooth. Drizzle the glaze over the cooled cake and scatter the chopped pistachios on top.