This creamy dish is the perfect side to chicken or fish, or as a meal on its own
In a 4-quart pot, melt 2 T. butter over medium-high heat. Add the onion and sprinkle with 1/2 tsp. salt. Cook the onion, stirring, until it softens and turns a light brown, about 3 minutes.
Add the rice and mushrooms and cook for about 1 minute.
Add the wine; increase the heat to high, and cook, stirring, until it almost completely reduces, about 1 minute.
Reduce the heat to medium; add 1 cup of the broth to the rice, and cook, stirring often, until the rice absorbs the broth, usually about 2 to 3 minutes.
Add another cup of the broth and cook until it's absorbed. Continue adding broth in this manner until the rice is creamy and tender, about 20 minutes total—you may or may not need all of the broth.
Toss in the arugula, cheese, all but a sprinkling of the chives, and the remaining 2 T. butter and stir until the arugula is just wilted, about 1 minute.
Serve immediately topped with black pepper and a sprinkling of chives.