Sift flour, baking powder, cinnamon, nutmeg, salt, cloves and ginger together in a large bowl.
Beat caster sugar, butter and brown sugar together in another bowl using an electric mixer until light and crumbly. Add eggs; beat for 1 minute. Add pumpkin puree, molasses, and vanilla extract; beat until well blended, about 1 minute. Blend in the flour mixture using the mixer or a wooden spoon until dough is sticky and incorporated.
Cover dough with waxed paper; refrigerate for 1 hour.
Preheat oven to 175 degrees C. Line 2 baking trays with baking paper.
Dip your hands into a small bowl of water. Shape the dough into two loaves that are 3cm high, 10cm wide, and 25cm long, Place each loaf onto a baking tray; top with pumpkin seeds.
Bake in the preheated oven until bottoms are dry, 20 to 25 minutes. Let cool for 5 minutes. Reduce oven temperature to 135 degrees C.
Transfer loaves to a flat work surface. Cut each into 10 diagonal slices about 5mm thick. Place sliced biscotti back on the baking tray.
Continue baking until light golden brown, about 20 minutes. Reduce oven temperature to 95 degrees C. Continue baking until dry, about 20 minutes more. Transfer to wire racks to cool.
For crisp biscotti, lower the oven temp to 75 degrees C and allow biscotti to remain in oven for another 40 minutes. At that time, turn off the oven and let cool inside oven for 1 hour.