Clumpy is not a word you would use to describe a perfect, cheesy pasta sauce. Smooth or velvety or sublime? Yes, those sound right. But clumpy? No. If your pasta sauce is clumpy, something is wrong, and it is likely the cheese.
Maybe not the actual cheese you are using. If it is something hard and crumbly like Parmesan or Pecorino or Grana Padano, you are probably fine in that regard. But there are some things you need to keep in mind when adding cheese to your pasta sauce to avoid unwanted textures. Here are the three things to ask yourself when adding cheese to pasta:
Is your cheese the right size?
When cheese is to be added to a pasta sauce, usually it is finely grated Parmesan. Cheese that is grated in large sheets or thick shreds will clump, because a larger amount of surface area allows for more cling potential. A larger piece of cheese also increases the chance that it will melt unevenly and onto other cheese surrounding it. Keep your cheese small and consistent in size for the highest quality melting.
Is there liquid in your pot?
Throwing grated cheese, regardless of size, onto dry pasta will give you a lumpy sauce. Well, not even a sauce. It will just give you globs of cheese. Hot liquids, like pasta water, heavy cream, melted butter, or beaten eggs, help distribute melted cheese evenly by surrounding it with heat. Since every bit of surface area is in contact with hot liquid, the cheese melts at the same rate. No clumps to be found, just a glossy, luscious sauce.
Are you adding your cheese all at once?
If you are, stop. Do not do it! Adding the sauce slowly, bit-by-bit, as you stir the liquid and pasta in your pot will make the cheese melt evenly and avoid clumping. Letting the cheese incorporate into the sauce little-by-little will guarantee that it stays smooth. Lighten the load. It will make everyone, including your sauce, happier.
Tomato N Cheese Pasta
1 cup uncooked small tube pasta
1 small onion, chopped
1 tablespoon olive oil
2 garlic cloves, minced
1 can (14-1/2 ounces) Italian diced tomatoes
1/2 teaspoon dried basil
1/2 teaspoon dried oregano
1/4 teaspoon sugar
1/4 teaspoon pepper
1/4 cup shredded part-skim mozzarella cheese
1/4 cup grated Parmesan cheese
Cook pasta according to package directions. In a small saucepan, saute onion in oil until tender. Add garlic; cook 1 minute longer. Stir in the tomatoes, basil, oregano, sugar and pepper. Bring to a boil. Reduce heat; simmer, uncovered, for 15 minutes. Drain pasta; stir into saucepan.
Transfer to a greased 1-qt. baking dish. Top with cheeses. Bake, uncovered, at 375° for 10-15 minutes or until cheese is melted.