Preheat your oven to 350°F (175°C). Grease a 9-inch pie dish or baking dish with some of the melted butter.
Scatter the raspberries evenly across the bottom of the prepared dish. If you're using frozen raspberries, don't thaw them beforehand.
In a large bowl, whisk together the flour, sugar, and salt.
In a separate bowl, whisk together the eggs, milk, and vanilla extract until well combined.
Gradually pour the wet ingredients into the dry ingredients, whisking constantly until the batter is smooth and lump-free.
Stir in the remaining melted butter into the batter.
Pour the batter evenly over the raspberries in the dish.
Bake in the preheated oven for 45-50 minutes, or until the clafoutis is puffed up, golden brown, and set in the center.
Let the Raspberry Clafoutis cool slightly before serving.