Bring broth and water to boil in medium pot on high heat. Add asparagus and cook until slightly tender, roughly 2 minutes.
Using a slotted spoon, transfer asparagus to bowl and set aside. Reduce heat to low.
Add farro to broth water mixture and cover. Cook until almost all liquid has been absorbed or farro is just al dente, stirring occasionally – 20 minutes. Watch closely to ensure farro is not overcooked or that the liquid runs dry too early. If farro is not cooked and liquid seems to have been absorbed add a 1/4 to 1/2 cup more water.
Meanwhile, cook pancetta in a Dutch oven (big enough to hold the farro) on medium heat until browned. After this, optional to remove half the liquefied fat. (I did)
Next, add butter and onion and cook 3 to 4 minutes in the Dutch oven. Add garlic and cook for 30 seconds. If farro is ready, add to the Dutch oven and cook for 1-2 minutes while mixing. If not ready, turn off heat until ready and resume.
Next add peas, tarragon, a dash of salt, and 1/4 teaspoon pepper to the Dutch oven and cook for another 2-3 minutes on medium heat.
Turn off heat. Stir in Parmesan, chives, lemon zest and juice, remaining 2 tablespoons butter, and reserved asparagus. Season with salt and pepper to taste. Serve immediately with additional asparagus and lemon juice.
Optional to add hot water in the end if you prefer to have a thicker saucy consistency rather than tumbling free farro grains!