Step 1

Grease a 14x10-inch oval baking dish with butter. Peel and core apples; cut them lengthwise into ¼-inch-thick slices. Melt butter in a skillet, and sauté apple slices gently until slightly brown. Turn off the heat; add rum, cinnamon, and ⅓ cup sugar. Toss and let stand 30 minutes.

Step 2

Put milk, remaining sugar, eggs, vanilla, and flour in a blender. Cover and blend till smooth, about 1 minute.

Step 3

Pour a thin layer of batter into the bottom of the baking dish, and bake just until batter firms. (It’ll be somewhat solid and dull-looking.) Spread apple mixture over batter; then pour in the rest of the batter. Place in the middle of the oven and bake for a little less than an hour. Clafoutis is done when it puffs and browns and a knife inserted into the middle comes out clean. Sprinkle a mix of cinnamon and sugar over the top; serve with whipped cream.