Heat 1 T each, butter and olive oil, in large saucepan over medium-high heat.
Add yellow onion to pan, sauté until fragrant.
Add peas to the pan and continue to sauté until they begin to soften, about 3 minutes.
Remove the contents from the pan, add the remaining butter and olive oil.
Add the garlic and shallot, sauté until fragrant.
Add the Arborio rice and combine well with the garlic and shallot.
To cook the risotto, add stock 1 cup at a time and let it cook out before adding next cup.
When the risotto is nearly there, add the salt, pepper and Parmesan to the rice. The risotto will seize up a bit from the cheese, add a little more stock if necessary.
Finally, add the peas and arugula back to the pan and toss to combine.
Optional: Serve with lemon.