Preheat the oven to 425 degrees F. Brush and evenly coat a 9-inch cast iron pan or deep-dish pie plate with the butter. Place next 6 ingredients in a bowl and mix until just combined. Add flour and mix until smooth. Pour batter into the pan. Arrange the pear slices in a fan-like fashion atop the batter. Bake in the middle of the oven 25-30 minutes, or until a golden crust has formed and a toothpick comes out clean when inserted and removed from the middle of the clafouti. Cool on a rack 20 minutes, and then dust with icing sugar. Cut into wedges and serve. If desired, serve with a dollop whipped cream or vanilla ice cream.