Combine farro and 4 cups of room temperature water in a bowl. Allow to soak for 30 minutes. Drain.

Bring broth to a boil in a pot. Reduce to a low simmer. Cover and keep warm.

While broth is heating, warm a sauce pot over medium-low to medium heat. Add 2 tbsp olive oil to pot, followed by onions. Season with salt and pepper. For best results, cook low and slow for a total of 20-30 minutes until onions are translucent, sweet and golden in color.

While onions cook, heat a large sauté pan over medium-high heat. Add remaining 2 tbsp olive oil. Add mushrooms, cooking in 2 batches, if needed to avoid over-crowding pan. Brown mushrooms on both sides for a total of about 10-15 minutes. After mushrooms brown, season with salt and pepper. Use additional olive oil, as needed, if cooking mushrooms in batches. Transfer to a plate until ready to use.

After onions are cooked, add in most of the mushrooms, reserving about 1/4 of the mushrooms for topping the risotto. Stir in farro and toast for about 3 minutes. 

Deglaze with wine. When most of the wine has reduced, add broth 1 ladleful at a time, stirring between each addition. Keep adding stock until farro is cooked through and you reach desired consistency, roughly 30 minutes. You may need slightly more or less broth than indicated.

Stir in parmesan cheese and butter. Agitate pan while stirring until a thick, creamy emulsion is achieved. 

If adding mascarpone, risotto should be a bit tighter than what is desired for the final result. Stir in mascarpone off heat. Taste and adjust seasoning, if needed. 

Scoop farro risotto into serving dishes. Top with reserved mushrooms, parsley and lemon zest. Enjoy.