Cut the tofu into cubes or strips and simmer them in water until firm, 4 to 5 minutes. Remove with a strainer and set aside.
Heat the butter in a wide skillet. Add the onions, celery, and fennel seeds and cook over medium heat until golden, about 10 minutes.
Add the paprika, flour, 1 teaspoon salt, pepper, and tomato paste. Stir well, then add the water and tofu. Bring to a boil, then lower the heat, cover, and simmer for 15 minutes.
Remove the lid, stir in the crème fraîche, and heat through.