Heat the chicken stock or vegetable stock in a pan and leave it on low heat to simmer. Set it aside. You will use this when cooking the risotto.
Heat a large pan with 1 tablespoon of butter at medium heat.
Add the shrimp and cook for 1 ½ to 2 minutes, until they get pink. Don't be tempted to cook any longer as they will cook more later with the risotto!
Remove the shrimp to a plate and add the olive oil to the same pan.
Add the shallots and garlic, and gently sauté for a few minutes until they are soft and translucent.
Add the rice and sauté for a few minutes until they are semi-translucent.
Pour in the white wine, and cook until all the alcohol evaporates.
Turn the heat to low and start adding the simmering stock a ladle each time.
Keep stirring the rice every few minutes, until the stock is totally absorbed by the rice.
Add more stock when there is no more liquid in the pan and repeat the same process until the rice is nearly cooked but still crunchy.
Stir in the mascarpone cheese, salt, and pepper at this point and cook for a few more minutes.
Check the rice and add more stock if necessary until it's cooked al dente. Add the cubed butter along with the peas and give it a good stir.
Stir in the shrimp, turn the heat off and add the grated Parmesan cheese on top. Do not stir the Parmesan cheese in, and let the risotto rest for 5 minutes with a lid on before serving.
Serve the risotto and garnish with chopped parsley or chives and extra grated parmesan cheese.