For the potato leek soup:

1. Peel and roughly chop the potatoes. Mince the garlic clove. 
2. Wash and thinly slice leeks; you only need the tender white and light green parts of the stem.
3. Heat the olive oil over medium heat in a large stockpot or Dutch oven.
4. Add the sliced leeks and chopped potatoes and cook for 5 minutes, stirring a few times. Add garlic and cook 5 more minutes, until the vegetables begin to soften and brown slightly. Be careful the garlic doesn't burn. 
5. Add the chicken or vegetable stock with the thyme and bring to a boil. Reduce the heat to low and simmer until the vegetables are tender and soft, 30 -35 minutes.
6. Blend until somewhat smooth using an immersion or hand blender; I like a little chunkiness in my soup so I didn’t blend it all I left a few potatoes chunks. But you can make it super smooth by blending it more and straining it before serving. 
7. Add the heavy cream and season with salt, pepper, and lemon juice.
8. Ladle into bowls and garnish with the mushrooms, sour cream and minced chives. 

For the mushrooms:

1. You can add some chopped mushrooms (1/3 of the amount) to the leek and garlic mixture in addition to the ones on top. The color of the soup will be grayish and the flavor will be earthier. 
2. Wash and immediately dry the mushrooms very well. Slice or coarsely chop them.
3. Heat the olive oil and add the mushroom pieces. Separate them so they fill the whole pan and cook over medium-high heat until beginning to brown. 
4. Let the water evaporate as you move them once or twice, but no more than that. Use immediately or refrigerate in a covered container or bowl for 3 days.