Step 1Toss plums with plum brandy or kirsch and 2 tablespoons granulated sugar in bowl. Let sit 30 minutes to 1 hour, tossing from time to time.
Step 2Drain liquid from plums and combine with milk and yogurt. Beat eggs with seeds from vanilla bean in bowl of electric mixer, or with whisk, until smooth. Add 4 to 6 tablespoons granulated sugar, depending on sweetness of fruit, and dash salt. Beat together. Slowly beat in flour, then milk mixture. Mix together well. (Ingredients can also be combined in blender and mixed at high speed.)
Step 3Arrange plums in greased 10- or 10 1/2-inch ceramic tart pan or clafoutis dish, rounded side up. Pour in batter.
Step 4Bake at 400 degrees until top is browned and clafoutis is firm, about 45 minutes. Press gently on top in middle to see if it is firm. If it isn't, return clafoutis to oven for about 5 minutes. Cool slightly on rack. Place 2 to 3 teaspoons powdered sugar in strainer and tap it above clafoutis to dust. Serve warm.