Fill pot with salted water [I use about a handful of salt to 5 quarts of water].
Chop onion. [About half a large or a whole medium onion. Too much is better than too little.]
In large skillet, saute onion in olive oil until golden. [Not brown.]
Stir in 12 oz tomato paste [2 small cans] and hot water. [At least as much water as tomato paste -- I use about twice as much.] Cover and simmer for _at least_ half an hour, stirring frequently.
When water boils, add pasta. [I use the curly one -- rotini or rotelle, but shells also work.]
When pasta is done, drain well. Then put in the pot. Stir in tomato sauce, one spoonful at a time. Sprinkle parmesan cheese over each spoonful of sauce. Stir well. Continue until sauce is gone. Dish up and serve.