Place spinach and mint leaves in a medium heat-safe bowl. Fill a separate large bowl with ice water and set both aside.
Bring 2 cups of water to a boil in small saucepan. Once boiling, pour over spinach and mint and let stand for about 30 seconds, or until leaves are wilted. Scoop leaves from hot water and drench in bowl of ice water. Stir until leaves are chilled, about one minute. Then remove from water, squeeze out excess moisture, and set aside on a paper towel lined plate.
Drain soaked cashews, rinse in fresh water until water runs clear, and drain again.
Place cashews in the food processor and blend for 1-2 minutes until a nut butter forms. Scrape down the sides of the bowl.
Add all other filling ingredients, except for spinach and mint, and blend until smooth and homogeneous, at least 2-3 minutes, scraping down the sides of the bowl as needed. Add spinach and mint leaves, then blend again until smooth and mixture is evenly green. Add more peppermint extract to taste. If you don’t mind little pieces of leaves in your filling (we don't), move to the next step. Or, you can stain the filling through a nut milk bag to remove the pieces.