Heat chicken broth in separate pot. Once hot, turn to simmer.
Melt butter and In a 10 inch stainless steel frying pan or an enamled cast iron small dutch oven. Add olive oil.
Add chopped onion and cook until translucent.
Add in dry arborio rice and toast for four minutes, stirring.
Add in cider vinegar. or wine. Continue to stir.
Have a lid ready to immediately cover when you put the first ladle of broth.
Add 1/2 cup broth. Cover for a few seconds to avoid any reaction from hot broth hitting the hot fat. Uncover.
Stir until the broth is nearly all absorbed in the rice.
Add another 1/2 cup broth and repeat until there is only 1/2 cup broth left to add.
Add in broth 1/4 cup at a time at the end, so as to not overcook the rice.
At the end of about 18 minutes, you should be at the end of the broth. Taste the rice. If it gives yet still has a bite, take it off. If it crunches, then cook another minute, stirring constantly. If you run out of broth and you're sure the rice is not done, add a small amount of water, (tablespoon or so).
Remove from stove, Stir in grated cheese. Season with salt and pepper.
Serve immediately. Garnish with chopped parsley.
This will serve 4 big servings.