Fill your largest pot 3/4 full with water and bring to a boil on high heat. Melt the butter and croutons in a skillet. Add the mustard and caraway seeds and stir over medium heat until the butter browns and smells nutty. Remove the skillet from the heat, but leave dressing in the pan. Add the salt and sugar to the boiling water and cook until dissolved. Place the cabbage in the boiling water and cook for 2 minutes exactly. Drain the cabbage in the bowl of the salad spinner or colander. Spin the cabbage to remove any excess water. Add the cabbage to the butter-crumb dressing and toss to coat thoroughly.;