Preheat the oven to 400 degrees F. Grease a 3-quart Dutch oven with 1 tablespoon butter, then sprinkle with 1 tablespoon sugar. Warm gently over low heat while you make the batter.
To a blender, add the eggs, milk, 2/3 cup sugar, vanilla, cardamom, cinnamon, salt and flour. Blend on high until a smooth batter forms, about 30 seconds.
Sprinkle the raspberries over the bottom of the preheated Dutch oven. Pour the batter over the raspberries and sprinkle the 2 tablespoons sugar over the top. Transfer the pan to the preheated oven; bake until the clafoutis is puffed and just set, about 30 minutes. Let cool in the pan for 10 minutes (it will deflate slightly).
Meanwhile, whisk together the yogurt and agave syrup in a small bowl. Dust the clafoutis with powdered sugar if desired. Serve with yogurt and chopped pistachios on the side.