Pre-heat the oven to 400 degrees F and position a rack in the center of the oven. Pour the melted butter into a 9-by-13-inch baking dish, and swirl the dish to coat the bottom and sides with the butter.

In a medium bowl, toss the raspberries with 1/4 cup of the sugar and then pour into the baking dish, spreading the raspberries evenly.

In a medium bowl, whisk the eggs together until blended. In a separate bowl, whisk together the remaining 1/4 cup sugar, the flour and salt. Whisk the sugar-flour mixture into the eggs. Then whisk the milk and the vanilla into the egg mixture. Pour the batter over the raspberries. Sprinkle the slivered almonds over the top, if using.

Bake the clafoutis for 40 to 45 minutes, or until it is golden brown and puffy. Let cool on a wire rack for about 30 minutes. Dust generously with confectioners' sugar and serve warm or at room temperature. Recipe inspired by Flour Cookbook by Joanne Chang