Prepare the Pistachios: Finely chop or grind the pistachios in a small bowl until you have a coarse consistency. This allows their natural oils and flavour to be released during cooking.
Make the Pudding Base: Combine milk and sugar with cornstarch in a medium saucepan, whisking over medium heat. It thickens quickly, so be sure to stir it continuously to avoid making lumps. Cook, stirring, for 5 minutes or until the pudding bubbles and becomes thick and creamy.
Add the Pistachios: After thickening the pudding base, reduce the heat to low and stir in the chopped pistachios and vanilla extract. Stir until the pistachios are well incorporated.
Cool the Pudding: Remove the saucepan from the heat and let the pudding cool for a few minutes. Then, transfer it to serving cups or bowls and cover it with plastic wrap, ensuring the wrap touches the surface of the pudding to prevent skin from forming.
Chill in the Refrigerator: Place the pudding in the refrigerator for at least 2 hours or until fully set.
Prepare the Grapes: While the pudding is chilling, wash and halve the grapes (or leave them whole if preferred). Set aside.
Assemble and Serve: Remove the pudding from the fridge once the pudding has been set. Top each serving with fresh halved grapes and a sprinkle of crushed pistachios if desired. For a sweeter touch, drizzle with a bit of honey.
Enjoy: Serve chilled and enjoy the creamy, nutty goodness of pistachio pudding with a refreshing burst of grapes!