Make the cashew-pepita milk: In a medium bowl, combine the cashews and papitas, then cover them completely with water. Cover the bowl with plastic wrap and allow to soak in the refrigerator overnight.
Strain the soaked cashew mixture, discard the soaking liquid and add the nuts to a high-power blender along with fresh water, the agave nectar and salt. Blend on high for at least 5 minutes to ensure a fine consistency, then put through a fine mesh strainer, makes 4 cups. The cashew milk will keep in the refrigerator for 2 to 3 days.
Make the vegan latte: Using a milk steamer or an espresso wand, heat the cashew milk to the manufacturer's' instructions and pour over espresso; serve hot.