Place baking sheet in oven. Cook compote over medium heat until liquid is reduced to medium-thick syrup, stirring occasionally, about 15 minutes. Whisk eggs, milk and vanilla in large glass baking dish until well blended.
Arrange bread slices in egg mixture.
Let stand until mixture is absorbed, turning once, about 5 minutes. Add 4 bread slices to skillet. Cook until golden brown, about 5 minutes per side. Transfer to baking sheet in oven. Repeat with remaining butter and bread slices.