Peel all the onions carefully.
Slice them into thin strips.
Make sure all slices are even.
This helps them cook at the same rate.
Heat butter and oil in your pan.
Add all the sliced onions at once.
Stir them well to coat with oil.
Cook on medium-low heat for 20 minutes.
Stir every few minutes to prevent burning.
Fill a large pot with water.
Add salt and bring to a boil.
Add your pasta and cook until tender.
Save 1/4 cup of pasta water before draining.
Drain the pasta in your colander.
Add the cooked pasta to caramelized onions.
Pour in the saved pasta water slowly.
Toss everything together for 2 minutes.
Add pepper and half the parmesan cheese.
Mix well until everything is combined nicely.
Put the pasta in serving bowls immediately.
Sprinkle remaining parmesan cheese on top.
Add fresh parsley for a pop of color.
Serve hot and enjoy your meal!