In a large saucepan, heat 3 tablespoons of the oil. Add the onion and cook over moderately high heat until softened, about 2 minutes. Add the garlic and cook, stirring, until fragrant, about 1 minute. Add the farro and stir until coated with oil, about 1 minute. Add the white wine and simmer until almost evaporated, 2 minutes. Lower the heat to moderate. Add 1 cup of the water and cook, stirring, until absorbed. Repeat with the remaining water, adding 1 cup at a time and stirring constantly until the farro is just tender and suspended in a creamy sauce, 30 minutes total.
Stir the tomatoes into the risotto and bring to a boil over moderate heat. Off the heat, stir in the remaining 1 tablespoon of olive oil and the cheese. Season with salt and pepper. Spoon the risotto into bowls, garnish with the basil and serve hot.
Rajat Parr pairs this dish with an appropriately casual wine, like a berry-rich Dolcetto d'Alba.