Place bread in a food processor; pulse 2 times or until crumbly.
Sprinkle crumbs on a baking sheet; bake at 350 for 5 minutes or until golden. (Breadcrumbs should measure 1 1/2 cups.) Set aside. Increase oven temperature to 37
Place potato in a Dutch oven; cover with water. Bring to a boil. Reduce heat; simmer 15 minutes or until tender.
Drain.
Melt butter in Dutch oven over medium-high heat.
Add onion and garlic; saut for 10 minutes or until browned.
Add milk, salt, and pepper; bring to a simmer over medium heat, stirring frequently. Reduce heat; simmer 3 minutes.
Place onion mixture in a food processor in batches, and process until smooth.
Add potato, and process until smooth.
Add 2 tablespoons chopped parsley and eggs; pulse 10 times or until combined.
Combine 1 1/4 cups breadcrumbs and 2 tablespoons chopped parsley; spread breadcrumb mixture into bottom of a 10-inch springform pan coated with cooking spray.
Spread potato mixture over breadcrumb mixture; sprinkle with 1/4 cup breadcrumbs.
Bake at 375 for 45 minutes or until golden brown. Run a knife around outside edge; cool 10 minutes.