How to Make It
Preheat oven to 450°F. Bring milk, butter, and salt to a simmer in a small saucepan over medium, stirring occasionally. Remove from heat. Using a wooden spoon, quickly stir in tapioca starch until well incorporated. (Dough will be very dense and dry.) Transfer dough to a bowl of a heavy-duty electric stand mixer fitted with the paddle attachment. Beat on medium speed until dough has cooled slightly, about 1 minute. Add eggs, 1 at a time, beating well after each addition. Stir in cheeses until combined.
Using a lightly greased 1 1/4-inch (about 1 tablespoon) scoop, drop spoonfuls onto parchment paper-lined baking sheets, leaving 1 1/2 inches between each. Place baking sheets in oven, and reduce temperature to 350°F. Bake until golden brown and puffed, 28 to 30 minutes. Serve immediately.