Chop the garlic clove and parsley into small pieces. Chop the walnuts, possibly toast them in a pan without fat until they are fragrant. Squeeze lemon juice.
Briefly roast the clove of garlic in olive oil over medium heat for about 30 seconds. Add approx. 600 ml water, stock cube and lentils and simmer for approx. 15 minutes over medium heat.
Take the saucepan off the stove and season sufficiently with salt and pepper. Add the sour cream and puree everything finely with a hand blender. Add 4 tablespoons of lemon juice.
Arrange the soup in plates and garnish with nuts and parsley.