Melt the butter in a large saucepan over medium heat. Cook and stir the onion and garlic in the butter until soft but not brown. about 5 minutes.

Pour the chicken stock into the pot and whisk in the tomato paste, heavy cream, and lemon juice. Turn the heat to high and bring the soup to a boil. Turn the heat down to medium-low, add the 3 cups of pecan pieces and the chopped chipotle peppers, and simmer the soup until the pecans soften, about 30 minutes.

Set aside 2 cups of soup. Pour the rest of the soup into a blender, filling the pitcher no more than halfway full. Hold down the lid of the blender with a folded kitchen towel, and carefully start the blender, using a few quick pulses to get the contents moving before leaving it on to puree. Puree in batches until smooth and pour into a clean pot. Alternately, you can use a stick blender and puree the soup right in the cooking pot.

Stir the reserved 2 cups of soup back into the pot and bring to a simmer and season with salt to taste. Serve, hot, with a sprinkle of chopped pecans for garnish.