Heat oil in a large pot over medium heat. Add the onion and cook, stirring occasionally until it softens and deepens in color. Season lightly with salt.

Melt the butter into the onions. Add the mushrooms and cook in batches until completely browned. This will take 20–30 minutes for the mushrooms to release their liquid and for the liquid to evaporate. Don't rush the process! Stir the mushrooms occasionally as they cook and continue cooking until they deepen in color. Adjust the heat as necessary to prevent them from burning.

Add the garlic and thyme to the mushrooms and stir to combine. Season with salt and pepper and cook for 1 minute.

Sprinkle the flour over the mushrooms and stir to combine—Cook for 2 minutes.

Add the stock in 1 cup increments and whisk after each addition. Continue adding and whisking until all of the stock has been incorporated—taste and season to your preferences. Bring to a boil and then reduce heat and simmer for 20 minutes.

Pour the heavy cream into the soup and stir to combine. Simmer for an additional 10 minutes and taste and season once more to your preferences.

While the cream of mushroom soup finishes simmering, prepare the mushroom topping. Heat the oil in a skillet over medium-high heat. Once hot, add the mushrooms and cook them in an even layer, about 4–5 minutes per side. Stir them occasionally to prevent them from burning.

Once the mushrooms are golden-brown all over, season lightly with salt and add the smoked paprika. Toss to coat and cook for 45 seconds. Turn off the heat and transfer them to a bowl.

Ladle the soup into bowls and garnish with the smoky mushrooms and minced chives. Enjoy!