In a large pot over medium heat, melt the butter. Add the chopped onion and sauté until soft and translucent (about 4–5 minutes). Then stir in the garlic and cook for another minute until fragrant.
Add the sliced mushrooms and cook, stirring occasionally, until they release their moisture and begin to brown (about 8–10 minutes).
Pour in the broth and stir in the thyme. Bring the mixture to a boil, then reduce heat and simmer gently for about 10–15 minutes to let flavors meld.
Remove the pot from heat. Either use an immersion blender to purée the soup to your preferred consistency — fully smooth, or partly blended for some texture — or carefully transfer to a blender and blend in batches.
Stir in the cottage cheese until well combined and the soup becomes creamy. Warm gently over low heat to integrate — avoid boiling after adding cheese.
Taste and adjust seasoning with salt and pepper if needed. Ladle into bowls, garnish with chopped parsley (or herbs), and serve warm.