Bratwurst with Mashed Potatoes and Cabbage

Name: Bratwurst with Mashed Potatoes and Cabbage
Ingredients: 1 1/2 pounds Yukon Gold potatoes, peeled and cut into chunks; Kosher salt; 1/4 cup extra-virgin olive oil; 6 tablespoons heavy cream; 1 teaspoon caraway seeds; 1/3 cup white vinegar; 4 teaspoons sugar; 4 cups thinly sliced red cabbage (from about 1/4 large cabbage); 1/2 small red onion, thinly sliced; 2 teaspoons country Dijon mustard, plus more for serving; Freshly ground pepper; 4 fresh bratwursts (about 1 pound); 1 12-ounce can lager-style beer