Bring the chicken broth to a bare simmer in a medium saucepan.
Heat 2 tablespoons of the butter and the olive oil in a large skillet over medium heat. Add the shallots and garlic, and cook, stirring, until softened, about 2 minutes. Add the Arborio, stirring to coat. Add the wine and simmer until evaporated.
Add just enough of the simmering stock to cover the rice. Cook, stirring constantly, until the rice is almost dry; adjust the heat to keep the liquid at a low bubble. Repeat with more stock to cover. Continue to cook in this manner until the rice is creamy and al dente, 20 to 25 minutes total; you may not use all of the broth.
Add the peas and cook, stirring, until heated through, about 2 minutes. Stir in the Parmesan, the remaining 2 tablespoons butter and the lemon juice and nutmeg. Add a splash more stock or water if necessary to loosen the risotto. Season with salt and pepper, and stir in the mint.
Transfer the risotto to a serving bowl, top with mint leaves and serve with additional Parmesan.