Preheat oven to 375 degrees F. Butter the bottom and sides of a 9-inch pie plate or eight 6- to 8-ounce custard cups or ramekins with the 1 teaspoon butter; set aside.
In a medium mixing bowl combine whipping cream, milk, eggs, flour, granulated sugar, melted butter, vanilla, almond extract, if desired, and salt. Using an electric mixer on low speed, beat until smooth. Arrange mixed berries in prepared pie plate or custard cups. Pour batter over berries. If using custard cups, place on a baking sheet.
Bake for 50 to 55 minutes for pie plate, 25 to 30 minutes for custard cups or ramekins, or until puffed and light brown. Cool for 15 to 20 minutes on a wire rack. Sift powdered sugar over top(s). Serve warm.