Soak cashews in filtered water to cover with pinch of sea salt for 2-4 hours. Drain and rinse before using.
In large stainless steel or cast iron lined pot such as Le Creuset, melt oil over medium low heat.
Add garlic and reduce heat to lower. Cook until softened and just starting to color, about 1 minute.
Add tomatoes and salt and raise heat to medium high. Cook stirring occasionally for about 5 minutes. Add stock or water, cashews, until spinach wilts. Remove from heat and transfer to blender jar. Reserve pot.