Meanwhile, melt 4 tablespoons butter in a pot over medium-high heat. Add the onion; cook until translucent, about 4 minutes. Add the rice and thyme; cook, stirring, until the rice is glossy, about 1 minute. Add the wine and cook, stirring, until the liquid is absorbed. Add 1 teaspoon Kosher salt. Ladle in the hot broth, about 1/2 cup at a time, stirring constantly, allowing all of the liquid to be absorbed before adding more. Continue until the rice is just tender, 20 to 25 minutes.