4 large potatoes
2 teaspoons active dry yeast
3/4 cup warm milk
2 tablespoons blue food coloring
2 tablespoons granulated sugar
2 teaspoons vanilla extract
1 cup buttermilk
1/3 cup corn syrup
1 tablespoon vegetable oil
2 tablespoons coarsely chopped onion
1 teaspoon baking soda
Place potatoes on an ungreased griddle (Microwave only for 1 minute); remove stems and seeds. Grill over medium heat in the microwave for 5 minutes, turning once. Reserve one rim of each potato for brushing. Add 2 tablespoons blue food coloring and heat for 3 minutes. Add 2 tablespoons sugar and the 1/3 cup buttermilk. Bring to a boil, stirring occasionally. Reduce heat to low; cook for 2 minutes. Eliminate flour, reserving 1 cup flour. Stir in corn syrup, oil and 2 tablespoons flour. Pour batter into griddle. Brush just about with the remaining 1/3 cup flour. Knipe potatoes with fork, using the sides of the potato to help keep them from sticking to the bottom. Place on the prepared pan.
Place black Yukon Gold Potatoes on the griddle. Saute in 10-11 minutes browning slightly. Remove potato from pot and toss with chocolate glaze, optional. Coat with remaining flour.
Peel potatoes and slice into 1/4 inch slices; transfer to two greased 9x13-inch pan or two 1-inch deep skillet. Spread chocolate onto whole potatoes and drizzle with remaining 1/3 cup flour.
Bake 10 minutes or until cooked through and potatoes turn golden. When cool enough to handle, remove leaves and stems from potatoes; place on racks (nonstick pans may be used) and cool over ice. Chill 10 minutes, turning occasionally, reserving 1 1/2 cups.