Potato And Onion Cakes
Ingredients 2 tablespoons unsalted butter, room temperature, plus more for tin Coarse salt and freshly ground pepper 3 teaspoons packed dark-brown sugar 3 teaspoons balsamic vinegar 3 teaspoons red-wine vinegar 1 1/2 teaspoons finely chopped fresh rosemary, plus tops of 6 sprigs 1 small red onion, sliced into six 1/4-inch thick rounds 2 medium Yukon Gold potatoes (about 1 pound), scrubbed 1 large egg yolk, lightly beaten Preparation Preheat oven to 400 degrees....