In large sauce pot, heat the olive oil over medium heat.
Sauté the onions until softened, about 3 mins.
Add in garlic and cook for 30 seconds.
Now, carefully add the stock and potatoes.
Bring to a simmer.
Continue to simmer, you may need to lower the heat, until potatoes are falling apart and fork tender about 10 - 15 minutes.
Stir in the spinach and cook for another two minutes.
Remove from heat and stir in lemon juice, cayenne pepper, and salt.
Pour into blender or Vitamix and blend until ultra smooth.
Taste and season again, if necessary.
Serve immediately hot. This may be enjoyed cold, too!