Preheat oven to 425°. Place butter in a 9-in. pie plate. Bake until butter is melted, 4-5 minutes. Meanwhile, in a large bowl, whisk eggs and milk. In another bowl, combine the flour, sugar and salt. Whisk into egg mixture until blended. Pour into prepared pie plate. Bake until sides are crisp and golden brown, 14-16 minutes.
Meanwhile, in a small saucepan, combine sugar and cornstarch. Gradually stir in orange juice and liqueur. Bring to a boil over medium heat, stirring constantly. Cook and stir until thickened, 1-2 minutes longer. Remove from the heat.
Spoon berries over pancake and drizzle with sauce. Dust with confectioners' sugar if desired.