Heat a large sauté pan over medium heat, add the oil and butter and when hot, add the onion. Cook until the onion becomes translucent.
Add the Arborio rice to the center of the pan and combine with the onion. Give it a stir so it gets coated with some of the oil in the pan.
Let it cook for a minute or two until it starts to give off a nice nutty aroma.
Start by adding hot stock to the pan about 1/2 cup at a time so the rice can slowly absorb the liquid. Stir frequently until the rice absorbs most of the liquid but before the rice starts sticking to the bottom of the pan.
Add another ½ cup of stock and keep stirring.
When you are down to about 2 cups of stock, add the shrimp and stir. Add some more stock. When the shrimp starts to turn pink, add the peas and a bit more liquid.If you need more liquid, and you’ve run out of stock, use a little of the hot water you had at the ready. You will need to taste the rice to determine when it reaches the right consistency for your palate.The shrimp cooks very quickly in the rice and stock so be careful not to overcook it.
Taste, and adjust seasonings with salt and pepper and serve.