To make the base: Add the hazelnuts to a food processor and process until it forms coarse crumbs. Drain the dates. Add the dates and almond butter to the food processor and process until everything is combined. The mixture should stick together when it is pinched between two fingers.
Line a 20cm (8-inch) square baking tin or container with baking paper. Press the mixture into the bottom of the tin/container to form a crust.
To make the filling: Add all ingredients to a blender and blend until combined. Pour the filling on top of the base and set it aside in the fridge to set for at least 6 hours.
To make the fruity topping: Add the mango and cornstarch to a small saucepan. Use a stick blender to puree the mango. Bring the mixture to medium-high heat and quickly whisk until thickened. Remove from the heat and add the passionfruit pulp. When the bars have set, spread the topping on the creamy layer. Set it aside in the fridge for at least 30 minutes to set further.
Remove the bars from the tin/container. Use a sharp knife to divide into servings. Enjoy immediately or store in an airtight container in the fridge for up to 5 days.