1 teaspoon (5 milliliters) pepper, plus more if required
8 cups (1.9 liters) beef stock
Olive oil, for drizzling
Juice of 1 lemon
Fried Sage Leaves (see recipe)
Preheat oven to 425 F (230 C).
Clean mushrooms with damp cloth. Remove woody stems and slice into 1.25 centimeter pieces. Set aside.
Toss mushrooms in half of the olive oil. Transfer to baking sheet and roast for 15 minutes. Reserve mushrooms with juices.
Heat butter and remaining olive oil in a large saucepan over medium heat. Add onion, carrots, celery, potato, and cook, stirring periodically, until moisture is released and onions start to brown. Add minced garlic, thyme, sage, pepper, and mushrooms and stir to combine. Add beef stock and simmer gently for one hour. Season with salt and pepper.
Remove from heat, then using an immersion blender, pulse soup until it is smoother but still has fine chunks of mushrooms (don’t blitz until completely smooth).
Divide soup between serving bowls. Drizzle with olive oil and lemon juice. Serve topped with Fried Sage Leaves (see recipe).