Add squash and sweet potato to a large skillet. Add enough water to just soften (not too much, or you get mush). Bring to a boil and simmer until tender, stirring frequently to prevent sticking. Drain off excess liquid and mash to form a puree. Add anise seed, salt and pepper. Transfer mixture to a large bowl, and stir in the flour. In a small bowl, add the yeast to the 1/4 cup of warm water. Set aside for 5 to 10 minutes until the yeast bubbles. Add to the potato mixture to make a firm dough, addding more water or flour as needed. Cover and let stand for 2 hours in a warm sport until the dough has doubled in size. Heat oil until hot. Ensure that the oil is hot enough by tearing off a small ball of dough, and pressing it into a ring. Drop the ring into the oil, being careful to avoid splattering. Fry until golden brown on each side, turning once during cooking. Drain on a paper towel. Adjust seasonings as needed, and then form the rest of the dough into rings and fry in batches until golden. Serve hot. Drizzle syrup or honey over doughnuts, if desired.