Place a 10-inch cast iron skillet on a rack about 6 inches below the oven broiler. Preheat the oven to 450 degrees F. Meanwhile, in large bowl, whisk together the brown rice flour, almond flour, tapioca starch, and salt. In a small bowl, whisk together the eggs, milk, and vanilla. Slowly add the milk mixture to the flour, whisking until smooth. Set the batter aside.
After about 20 minutes, when the skillet and oven are hot, carefully remove the pan and switch the oven to broil. Add the butter to the hot skillet and swirl it around. Sprinkle the sugar evenly over the butter. Add the pear slices and vanilla bean seeds and toss to coat.
Return the skillet o the oven and broil until the sugar begins to caramelize, stirring halfway though, 4 to 5 minutes. Remove the skillet from the oven and turn the oven temperature back to 450 degrees F.
Whisk the batter and immediately add it to the skillet. Return the skillet to the oven and cook until the Dutch baby is puffed and set, about 12 to 16 minutes. Sprinkle it with confectioners’ sugar before serving.