Pappardelle with Bacon and Gruyère

In a pot of boiling salted water, cook chard 1 minute. Reserving water, transfer chard to a colander, squeeze out excess water and chop. In a large skillet, heat olive oil over medium heat. Add bacon, chopped, and cook until browned, 4 minutes; transfer to a bowl. Reduce heat to low, add garlic and cook until fragrant, 2 minutes. Add wine and simmer until reduced by half, 3 minutes. Add heavy cream and sage and simmer 2 minutes. Add salt and pepper and reserved chard, cover and remove from heat. Return pot of water to a boil and cook pappardelle according to package instructions. Drain and add to skillet. Over medium heat, toss pasta with sauce, Gruyère and reserved bacon until cheese starts to melt, 1 minute. Divide among 4 bowls and top with walnuts.