In a wide pot or rondeau pot, add the pancetta and turn the heat to medium. Cook, turning occasionally, for 6-8 minutes or until the fat has rendered and the pancetta is crispy. Using a slotted spoon, transfer the pancetta to a bowl.
Cook the Aromatics:
If the pot seems dry, add a slick of oil. Add the onion and fennel and cook, stirring occasionally, for 8-10 minutes or until well-browned all over. Season with salt and pepper and transfer to a bowl.
Brown the Mushrooms:
Add half the butter to the pot. Once melted and frothy, add half the mushrooms. Stir often and cook the mushrooms until they are well-browned and beginning to crisp up. This will take a good 10-15 minutes. Season with salt and pepper and transfer to the bowl of onions.
Melt the remaining butter in the pot and brown the remaining mushrooms and season with salt and pepper.
Assemble the Soup:
Add the bowl of mushroom, fennel, and onions to the pot and season to taste with salt, pepper, garlic powder, Espelette powder, dry thyme, dry parsley and paprika. How much you use is up to you; I used a few generous shakes of each spice!
Turn the heat to medium-high and stir often until fond begins to form on the bottom of the pot. Add the white wine to deglaze the pot and scrape up the fond from the bottom. Bring to a boil and cook for 5-6 minutes until reduced slightly.
Add the chicken stock and bring to a boil again. Reduce heat and simmer for 30-40 minutes. Taste and season again to your preferences.
Prepare the Trumpet Mushroom Topping:
Turn the broiler on.
Slice off a few rounds from each of the stems of the trumpet mushrooms. Cut the remainder of each mushroom in half lengthwise.
Add oil to a skillet and turn the heat to medium-high. Add the mushroom rounds in an even layer and arrange the trumpet mushroom tops in an even layer around the stem rounds, cut-side down. Cook without moving for 5 minutes. Flip the mushroom tops and rounds and transfer to the broiler for 4-5 minutes until beginning to char and turn golden brown. Remove and transfer to a plate, season with a sprinkle of salt, and keep warm.
Finish the Mushroom Soup:
Using an immersion blender, blend half the soup until puréed. Add as much cream as you like and stir to incorporate. Taste and season the soup once more to your preferences.
Ladle the soup into bowls and garnish with the reserved pancetta, crispy trumpet mushrooms, and reserved fennel fronds. If desired, drizzle with a touch of extra virgin olive oil. Enjoy!