In a large pot, warm the olive oil over medium-high heat, then add the onions. Stir, then reduce the heat to medium-low and let them soften and caramelize a bit, at least 10 minutes and up to an hour.
Add the garlic and stir for a minute, then add the sweet potatoes and stock and increase the heat to medium-high. Bring to a boil and cover, reduce the heat to simmer for 10 minutes.
When the sweet potatoes are tender, stir in the kale, cover the pot, and simmer for 3 minutes.
Uncover the pot, stir in the spinach, and cover. Simmer for 2 minutes.
Transfer the contents of the pot to a blender and puree. Season to taste with lemon juice.Serve warm, sprinkled with almonds.
FOR GARNISH: Place the sliced almonds in a small saute pan and swirl over medium-high heat until lightly golden, then transfer to a bowl to cool.