Place a cast iron skillet on a rack about 6 inches below the oven broiler. Preheat the oven to 450 degrees F (230 degrees C).
Meanwhile, in large bowl, whisk together Brown Rice Flour (1/4 cup), Almond Flour (1/4 cup), Tapioca Starch (3 tablespoon), and Kosher Salt (1/4 teaspoon).
In a small bowl, whisk together the Large Egg (3), Milk (3/4 cup), and Vanilla Extract (1/2 teaspoon). 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 Unsalted Butter (2 tablespoon) to the hot skillet and swirl it around. Sprinkle the Granulated Sugar (2 tablespoon) evenly over the butter.
Add the Bosc Pear (1) and the seeds of the Vanilla Bean Pod (1). Return the skillet to the oven and broil until the sugar begins to caramelize, stirring halfway through, 4-5 minutes.
Remove the skillet from the oven and turn the oven temperature back to 450 degrees F (230 degrees C). Return the skillet to the oven and cook until the Dutch baby is puffed and set, about 12-16 minutes.
Sprinkle it with Powdered Confectioners Sugar (to taste) before serving.