Preheat oven to 350 degrees; butter a 9-inch pie dish. Peel, halve, and core 3 Comice or Bartlett pears; slice 1/4 inch thick lengthwise. Arrange slices, overlapping slightly, in dish.
In a blender, process 1/4 cup melted unsalted butter, 1/3 cup each granulated sugar and all-purpose flour, 2 teaspoons vanilla extract, 3 large eggs, 3/4 cup milk, and 1/4 teaspoon salt until smooth.
Pour batter over pears; bake until golden and firm to touch, 40 to 45 minutes. Serve warm or at room temperature, dusted with confectioners' sugar.