In a large saucepan, add your olive oil and butter over medium heat. Once hot, add your minced garlic, thyme, and diced onions. Cook for 5 minutes until translucent.
Turn the heat on high and all your sliced mixed mushrooms. Cook until soft and golden. Hold a few spoons of mushroom on the side to garnish at the end.
Add your chicken stock and bring to a simmer for 30 minutes. Transfer your soup to a mixer and blend until smooth. If it seems too thick, thin it out with a bit of chicken stock. Season with salt and pepper. Garnish with cooked mushrooms.