Preheat the oven to 180 C (350 F) and line a baking tray with parchment paper. Either blend the pistachios in a food processor or chop them by hand until fine and mealy. In a bowl, stir together the pistachio meal, almond meal and baking soda. Add the coconut oil and syrup then use your fingertips to rub the oil into the nuts and combine all the ingredients. Spread out on the baking tray and bake for 4-7 minutes until the crumbs near the edge of the pan are starting to brown. Let cool before serving with the ice cream. Store any leftover crumb in an airtight container.