Season chicken thighs with salt and heat olive oil in the pan. Fry chicken thighs until golden brown and set aside. Add onions, crushed garlic, fennel bulb to the pan. Reduce to medium-low heat and cook until soft.
Add fennel seeds and bay leaf to the pot. Cook until fragrant. Add the chopped tomatoes, chicken stock and 2 cups of water. Increase to high heat and bring it to a boil.
Add in reserved chicken thighs to the pot along with thyme and the parmesan rind.
Reduce flame to medium heat and stir soup occasionally for 1 hour and 15 mins.
Heat olive oil in frying pan on medium heat. Add in sourdough bread and top with parmesan cheese. Cook until golden and add fennel fronds.