Place the chicken broth in a medium saucepan and bring to a low simmer over medium heat. Once simmering, reduce the heat to very low and keep warm.

In a large Dutch oven or heavy bottomed pot, melt the butter over medium heat until it is lightly bubbling. Add the finely chopped onion along with a generous pinch of kosher salt. Sauté over medium low heat, stirring often, until the onion is very soft and translucent, about 5 to 7 minutes.

Increase the heat under the pot to high. Add the sliced mushrooms and stir to combine. After a minute or so, the mushrooms will begin to sweat and release their liquid. Continue to cook for an additional 2 to 3 minutes, stirring occasionally, until the mushrooms have softened and started to turn golden. Add the chopped garlic and fresh thyme. Sauté, stirring continuously, until fragrant, about 30 seconds. Season the mixture to taste with kosher salt and freshly ground black pepper.

Add the farro to the pot. Toast the grains over medium high heat for 1 to 2 minutes, stirring continuously. The farro will crackle lightly, and the pan should become mostly dry.

Pour in the dry white wine. Cook over medium high heat, stirring every so often, until the wine has been completely absorbed by the farro, about 2 to 3 minutes.

Add the optional Parmigiano Reggiano rind and all of the hot chicken broth to the pot. Stir to combine thoroughly. Bring the liquid to a boil, then immediately reduce the heat to a steady simmer. Cover the pot and cook for 45 to 50 minutes, stirring roughly every 15 minutes, or until the farro is tender but still slightly chewy at the center and the risotto has thickened. Note: For the final 5 to 10 minutes of cooking, I recommend removing the lid to help the excess liquid reduce and thicken the risotto more easily.

Reduce the heat to low. Stir in the ¾ cup of freshly grated Parmigiano Reggiano cheese and the lemon juice until well combined. Gently fold in the thawed peas. Taste the risotto and season with additional kosher salt and freshly ground black pepper as needed. (If it tastes flat, a generous pinch more of salt often does the trick.)

Remove the pot from the heat, cover, and let the risotto sit undisturbed for 5 minutes. This resting time helps it thicken further and develop an even creamier, more classic risotto like texture. Remove and discard the Parmigiano Reggiano rind, if used.

Serve the risotto in pre warmed bowls. Garnish generously with fresh thyme leaves, finely chopped flat leaf parsley, and additional freshly grated Parmigiano Reggiano cheese.