My husband loves Italian sausage and spicey, so this is what I tested out and it came out just perfectly. It's spicey but if you want it really hot just add more red pepper flakes and adjust to your own spicey senses. This recipe is just kicked up enough for my husband. Enjoy
Remove the sausages from the casings and crumble. Put a little olive oil in bottom of a large pot and start to brown and crumble until all redness is gone. Usually takes about 10 minutes. Remove with slotted spoon and leave fat in the pan. To the remaining fat in the pan add the onions and garlic on low heat until soft, about 3 or 4 minutes. Add the fennel seeds, salt and red pepper flakes, saute still on low, stirring until fragrant. Add the tomatoes, all the juices too and tomato paste, oregano and cooked sausage and fresh basil cook and stir until thick and fragrant. Leave on a low flame for 45 minutes. Taste and adjust seasoning to your taste.
Meanwhile, cook pasta in boiling salted water. Drain and toss with the sauce. If you desire to add ricotta do that or just top with grated cheese.