Preheat a 12″ cast iron skillet on medium-high heat.
Brown Italian sausage. If using onions, put them in with the sausage.
Drain grease.
Add tomato sauce and diced tomatoes.
Add spices. Crush dried parsley and oregano leaves in your hand to release the flavor before putting them in the pot. Chop fresh basil and add that, too.
Bring sauce to a boil, then cover (leaving the lid slightly ajar) and reduce heat to simmer.
Your pasta water should be boiling. Add 1/4 cup salt to pasta water and stir to dissolve.
Boil thin spaghetti according to directions.
Drain pasta.
Serve. I serve my noodles and meat sauce separately, but some people combine the sauce and pasta. Put parmesan cheese on the table so diners can add their own.
Parmesan Toast
Preheat your broiler when you start the sausage.
Place bread slices onto a foil-lined half sheet pan. Defrost 1/2 stick butter for 45 seconds and stir in 2 cloves of minced garlic.
When your sauce is ready, spread garlic butter over the bread. Grate Parmesan cheese on top of the bread.
Pop it into the broiler when the pasta has about 5 minutes left on the timer. Keep an eye on it and rotate it periodically, then pull it out when the cheese is melted and golden brown but before the crust begins to burn.