Maybe more so than other foods, potatoes need salt. Instead of salting the water they boil in, sprinkle the potatoes with salt after draining. Then salt the white sauce separately for the most pronounced flavor.
Place potatoes in a large saucepan; cover with water. Bring to a boil. Reduce heat; simmer 5 minutes or until potatoes are almost tender. Drain. Sprinkle potatoes evenly with 1/4 teaspoon salt; set aside and keep warm.
Heat a medium saucepan coated with cooking spray over medium heat. Add shallots; cook 2 minutes or until tender, stirring frequently. Lightly spoon flour into a dry measuring cup; level with a knife. Sprinkle flour over shallots. Gradually add 1/2 cup milk, stirring with a whisk until well blended. Gradually add remaining 1 1/2 cups milk, stirring with a whisk. Cook over medium heat 9 minutes or until thick, stirring frequently. Remove from heat; stir in 3/4 teaspoon salt, Asiago, chives, pepper, and bacon.
Arrange half of potato slices in an 8-inch square baking dish coated with cooking spray. Pour half of cheese sauce over potato slices. Top with remaining potato slices and cheese sauce; sprinkle with Parmesan. Bake at 350° for 35 minutes or until cheese is bubbly and lightly browned.