Lightly toast the walnut and cashews in a medium oven for 5 minutes, pick the basil leaves from the stems and place them in a blender with the garlic, half of the oil and lend them to a puree. Add the rest of the spinach, oil and nuts to blend. Add Salt and pepper to taste. Store for up to two weeks in a sealed container in the fridge, or freeze for up to 6 months.