In a large Dutch oven over medium, melt the butter. Add the rice and cook, stirring occasionally, until lightly browned at the edges, 2 to 3 minutes. Stir in the cardamom and salt, then cook until fragrant, about 30 seconds. Pour in the milk, bring to a simmer and cook, uncovered, stirring occasionally and adjusting the heat as necessary to maintain a gentle simmer, until the rice is tender and the mixture is creamy, 20 to 25 minutes.