Peel the pears and cut the bottom off each to give a flat base – cut them to a height that will fit snugly in your tin. Use a melon baller or small knife to cut out the pips from the base. Roughly chop the pear scraps, discarding the pips, and set aside. Tip the sugar, cinnamon, star anise, cloves, zests and 600ml water into a saucepan large enough to fit all the pears. Bring to the boil, then simmer until the sugar has dissolved. Add the pears, cover with a lid or a piece of baking parchment, and poach gently for 15 mins until a knife easily slides into a pear. Leave to cool in the liquid.
Now make the sponge. Put the dates and linseeds in a saucepan and add the almond milk. Bring to a gentle simmer, then cook for 2-3 mins until the dates are soft. Pour into a food processer and blitz until smooth. Add the oil and blend again, then scrape into a bowl and set aside to cool a little. Heat oven to 180C/160C fan/gas 4. Grease and line a 20 x 30cm baking tin (a loose -bottomed one if possible) with a strip of baking parchment.
Put the dry ingredients in a large mixing bowl with 1/ 2 tsp salt. Mix well, breaking up any lumps of sugar with your fingers, and shaking the bowl a few times to encourage any remaining lumps to come to the surface. Add the date and oil mixture, and stir well. Fold in the chopped pear scraps. Scrape the cake mixture into the tin, then nestle in the pears, standing straight up, so that the bottom halves are covered. Bake for 35-40 mins until the cake is cooked through. Insert a skewer to the centre to check – it should come out clean. If there is any wet cake mixture on the skewer, return the cake to the oven and bake for 10 mins more, then check again.
Meanwhile, bring the pear poaching liquid back to the boil and simmer until reduced to a glossy syrup. When the pudding is cooked, cool for 5-10 mins, then brush all over with the syrup, saving a little extra to serve alongside, with vegan ice cream, if you like.