Sift 175g flour and 1 tsp baking powder into a large bowl.
Whisk 175g sugar, 175g butter, and 3 eggs for 4 minutes until thick.
Fold 75g chopped pistachios into the batter.
Butter a 1.2-litre basin and place 3 tbsp treacle and 8 figs in the bottom.
Pour the batter into the basin and level the surface.
Cover the basin with a round of greaseproof paper.
Secure a pleated piece of foil over the bowl with string and trim excess.
Steam the basin in a large pan of water for 2 hours.
Boil 750ml cream, 250ml milk, and 225g sugar in a pan.
Whisk 11 egg yolks in a separate bowl for 2 minutes.
Slowly pour the hot cream onto the eggs while whisking constantly.
Heat the custard until thickened, sieve, and cool in iced water.
Blend 100g pistachios and 3 tbsp rum into a fine paste.
Stir the pistachio paste and remaining chopped nuts into the custard.
Churn the mixture in an ice cream machine until set.
Serve pudding wedges with a scoop of pistachio ice cream.