Preheat oven to 350°. Cook pasta according to package directions for al dente.
In a Dutch oven, brown sausages on all sides, about 5 minutes. Reduce heat to medium-low; add water. Cook, covered, until a thermometer reads 160°, about 10-15 minutes. Remove from pan; slice sausages.
In the same pan, melt butter over medium heat. Stir in flour until smooth; gradually whisk in cream. Bring to a boil, stirring constantly; cook and stir until thickened, 1-2 minutes. Stir in mozzarella and Parmesan cheese until melted; remove from heat.
Meanwhile, in a large bowl, whisk eggs and milk until blended. Stir in basil, fennel seed, garlic, salt, pepper and cooked sausage. Add to Dutch oven. Drain pasta and add to cheese mixture immediately; toss to coat. Sprinkle with Romano cheese. Bake, uncovered, until a thermometer reads 160°, 20-25 minutes. Sprinkle with additional basil.