Step 1: Place the whole mandarins in a small pot of water and boil for 40 minutes until soft. Drain and let cool slightly.
Step 2: While mandarins boil, soak the chopped dates in 1/2 cup boiling water for 15 minutes, then mash into a rough paste.
Step 3: Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.
Step 4: Cut the boiled mandarins in half, remove any seeds, and blend the whole fruit (including skins) into a smooth puree.
Step 5: In a large bowl, cream the butter and sugar together until light and fluffy. Add the eggs one at a time, beating well.
Step 6: Stir in the mandarin puree and the date paste into the wet mixture.
Step 7: Sift the flour, baking powder, baking soda, and salt. Fold the dry ingredients into the wet batter until just combined.
Step 8: Pour the batter into the prepared pan and sprinkle the chopped pistachios evenly over the top.
Step 9: Bake for 45-50 minutes, or until a skewer inserted into the center comes out clean.
Step 10: While warm, brush the top of the cake with honey or extra mandarin juice for a sticky finish. Let cool before slicing.