Brush four 4-ounce ramekins with butter. Sprinkle brown sugar in the bottom of each and line with sliced pineapple. Whisk 1 egg, 1/4 cup buttermilk, 3 tablespoons melted butter and a dash of vanilla in a bowl, then stir in 1/2 cup flour, 6 tablespoons granulated sugar, 1/2 teaspoon baking powder, 1/8 teaspoon baking soda and a pinch of salt. Divide among the ramekins. Bake at 350 degrees F, 20 minutes. Let cool, then unmold and top with confectioners' sugar.