Melt the butter in a large saucepan over medium-low heat; cook and stir the onions in the melted butter until translucent, about 5 minutes. Stir in the beef and season with salt and pepper. Cook, stirring occasionally, until the meat is tender and the juices have cooked away, about 30 minutes.
Stir in the garlic and peas; pour in enough water to cover. Bring the mixture to a boil, cover, and simmer over low heat until the peas change color and are tender and hot, and almost all of the liquid has been absorbed, about 1 hour.