"I started throwing ingredients together on a cold wintry day - this fabulous thick and warming soup was the result. The fennel adds brightness and provides a nice contrast to the hearty beans and the heat of the crushed pepper."
Heat oil in a large pot over medium heat. Add fennel and onion; cook and stir until slightly softened, about 5 minutes. Stir in garlic; cook until fragrant but not browned, about 2 minutes.
Pour vegetable stock, black beans, diced tomatoes, red pepper flakes, pepper, cumin, thyme, and bay leaves into the pot. Bring to a gentle boil; reduce heat and simmer, stirring occasionally, until fennel is tender, 35 to 45 minutes. Add spinach, stirring to separate leaves; simmer until heated through, 1 to 2 minutes.