Place the cannellini beans, cumin, measurement water, oil, soured cream and garlic in a food processor or blender and blend until smooth. Season to taste. Transfer to a serving bowl and set aside.
Make the pesto. Heat a small, dry nonstick frying pan, add the pumpkin seeds and dry-fry for 2 minutes until very lightly toasted. Leave to cool, then chop the seeds until small. Alternatively, whizz the seeds in a mini food processor. Stir together the chopped seeds, the oil, coriander, lime juice and rind in a bowl and season to taste.
Swirl the pesto over the white bean dip and serve with crispy tortilla chips.